I went with 7.1.1 Update 3 Pro

(That is a mouthful)

How hard is it to dual-boot a mac?

It might be neat,seeing how some apps love 7 and some are crazy-fast on 6.

7.1.1 Pro is pretty fast, and reflects what the oringal oner would have been using. 6 seems to old to me. I dont know why. A machine I would run 6 on is a Plus or SE. Anything 32 bit gets 7.