XPx32 v XPx64 v Vistax64

[geno]

Before I get into this, I did indeed read this thread.

That said, my situation is slightly different. Some background: For quite awhile I was stalling about getting a new computer, as my old was getting quite outdated. Finally I purchased all the parts from Newegg last week (save PSU which was recently replaced to accomadate a full system upgrade and a case which is more than adequate) and put it all together yesterday. Unlike that other thread, my new computer is sitting in my room right now, waiting for its operating system. So in that respect, I don't mean for this thread to be focused around the hardware of my new rig (I will put specs in at end though).

Now to my dilemma. When I purchased the parts, I noticed a pretty huge sale on 4GB set of DDR2 1066MHz Corsair Dominator RAM. It cost nearly the same as the 2GB I had been planning on and I figured why not. Now when I made this purchase, I had completely forgotten about the RAM limit for 32bit systems. Not wanting to make at least half a gig of my RAM a waste, I decided to take a look at upgrading my OS. As a sidenote, the rest of my hardware is 64bit ready from what I've seen on the boxes, so I don't think drivers for most of it will be a big problem.

So here's where I've got my decision.

In my mind I've gotten my choices down to XP x32 and Vista x64 (after reading better things about compatibility for that than XP x64). I haven't completely taken it off the table though if anyone has a particular reason why I should go with XP x64. If I go with a 32bit system, I'll stick with XP (which is why Vista x32 isn't in the title). I've read plenty of complaints about both Vista and 64bit systems and the hassles they can cause, but most of what I've seen has some sort of solution or work around. I'm more than willing to do these fixes as long as future SPs and games begin to make both Vista and 64bit systems not only tolerable, but preferrable. I figure Vista is only going to get better with time as microsoft continues fixing and improving it, especially now that they've stopped selling XP.

At the same time, I've been using XP pro x32 for so long, I'm really quite used to it. A little over 3GB of RAM is nothing to laugh at anyways, and (assumably) if I ever want to take advantage of the 4GB with a 64bit system, I can upgrade later. One of the main issues I have with this option though is that my RAM's warranty doesn't cover 32bit systems and (according to its guide) wasn't designed to be used for anything but x64.

So I have some positives and some negatives for both options. While I don't always play the newest, most demanding games, I am a pretty big multitasker while playing the games I do (and don't get me wrong, I do plan on playing newer games with this comp). So in that respect, having 4GB wouldn't be a complete waste on me.

All of this brings me to a couple questions that weren't really covered well or were sidetracked in that other thread.
1. Beyond the extra RAM, how much of a benefit is there in a 64 bit system? From what I've read, there isn't much outside of the future expectations of games and apps that will take advantage of it.
2. I know people are often quick to jump on the downsides of Vista, but I would be interested in hearing about the practical improvements that the OS does offer that people actually appreciate. Keep in mind, x64 driver compatibility and DX10 + its future possibilities are pretty much the biggest (if not only) things that really keep me interested in Vista right now.
3. Any additional positives and negatives for both Vista vs. XP and 32bit vs 64bit.
4. Knowing my specs and situation, which OS would you go with and why? Remember, I'm unlikely to make any hardware changes at this point (upgrades or downgrades) so work with what I got.

Specs:
Processor: Intel Core 2 Duo E8400, LGA775
Mobo: Gigabyte S-Series GA-P35-DS3L
Graphics Card: Sapphire Radeon HD 4870 (512MB/GDDR5)
RAM: Corsair Dominator 2 x 2GB DDR 1066MHz
HDD: 500GB Wester Digital SATA 7200RPM 3.0GB/s 16MB Cache
PSU: Antec 650W ATX12V v2.2 (didn't buy on newegg, but I believe its this.)
Onboard sound.
Cooling should be fine.
Not planning on overclocking.

Thats about it. Help me make a decision!

[Reality]

well, vista's version of prefetch is much better than XP's which will in turn utilize your 4GB of ram better than XP x64 would, on bootup all of my ram is cached full of the applications that I use most often, which of course increases the speed at which applications load

practical improvements of vista, well for one Explorer is amazing now, the dropdown menus in the path bar, each directory (i.e. C:\Program Files\Square Enix\Playonline) is clickable making accessing those individual directories easier via just clicking them in the path, instead of hitting the back/forward buttons until you find which folder you're looking for, along with other useful GUI improvements). I already mentioned the more advanced data prefetching in vista. And obviously, DX10 access for games that utilize it is a huge bonus, something you'll NEVER have under Windows XP

with those specs, I'd go Vista x64 Ultimate, which is what I'm currently using. if i can make a suggestion, make a small partition for your operating system on that 500GB drive, something around 50-60GB (to have space for things like default save game files that sometimes automatically save to My Documents, as well as large windows updates, along with some programs that do not let you choose the default path). this will increase startup time as the drive's spindle will only have to move across a smaller part of the drive to access operating system files, rather than over the whole drive

[geno]

Thanks for the advice. I'd been planning on a small windows partition already as my last HDD was so much more cluttered and slow and reformatting became such a bitch that I just wanted to avoid it at all costs. By the end of my old computers life, I had eventually taken to storing my media on my brother's 400gb over the network and avoiding too many new program installs if I could so I doubt it will take me long to get used to a separate partition for Windows alone.

As for OS troubles, I was also tending to lean towards Vista Ult x64 by the time I got to sleep. Even ignoring the improved RAM usage, the OS just seems like it will only become better with time. Even if there are some compatibility issues with older games or apps initially, I'd rather deal with those than not be able to take full advantage of my graphics card and rest of my system on DX10 games in the future.

While I think I'm already likely to stick with Vista Ultx64, I'd still appreciate more input on this from the XP enthusiasts side (I know there are plenty out there). Thanks.