Max temp for 720 is 73C. Keep it below 65C and you'll be fine.
My 720 BE won't run stable with the 4th core enabled. You mileage may vary as some 720s have flawed cores and others are just 820s with a core deliberately disabled.
Updating the BIOS on pretty much any modern Gigabyte board is very easy. Get a flash drive, format it FAT32,
download the BIOS for your motherboard, run/extract it to your USB drive, reboot, and then press "END" at the POST screen (or whatever your board wants to start the Q-Flash utility), then just follow the prompts. Once the system reboots, go into BIOS and load the optimized defaults, then reset everything to what you want/need.