I've been playing with and parsing mine against hagun for a while now, and I'm no math pro but I'll do my best to answer.
Hagun 6-hit outparses pachi 5-hit, albeit not by a lot.
I parsed out about +120 WS damage/ws on hagun (818.4) over pachi (698.0), and pachi (97.9) beat hagun (87.08) by 10 damage per melee hit (all on greater colibri).
I'm only so-so on math so I don't really want to delve into it too much, but the problem arises from adding meditate into the works, since meditate strongly favors hagun over pachi due to the free WS damage. Each meditate gives hagun +120 damage, and if you have AF head and AF2 hands, it's another half a WS, or +60 more damage over pachi. Also, hagun has the delay advantage, so while it only takes 5 hits for pachi to get 100 tp, 6 hits from hagun comes pretty close in real-time.
I also give up dusk gloves (3% haste) to maintain 5 hit with hachiman kote because I don't have usu body.
I did make an alla post hoping for some math on 5 hit pachi vs. 6 hit hagun, and you can see it
here. Milich had some good info to offer, and it looked like solid math to me (but like I said, I'm no math genius).
tl;dr - getting 20 tp/hit is very fun. As far as my gear goes (usu feet but no body), hagun wins by a little bit, and pachi falls somewhere below hagun, but above soboro, ushi, onimaru, etc. for meritting. If I had an usu body (and could therefore 5-hit in dusk gloves), the results
might be different, but I doubt it.
Either way, at least it looks cool.
http://i107.photobucket.com/albums/m...803_214811.png