My guess is that you'll be able to upgrade to OS6 without a problem. The limitation for us lowly OS4x users is that we have ye olde dragonball processors. Real snails comparatively....
My SO wants a new pda now too, so of course I'm "in charge" of this purchase. I'm hesitant to get anything right now with all the pre-holiday releases coming up cuz we all know they'll be in overstock sale by 2/1. Oh how I wish there was a good strategy for buying something decent and affordable while simultaneously avoiding the whining I'll endure!
My guess is that my upcoming/future pda lifestyle will be comprised of buying something, upgrading within a year (6 months?), and selling my stuff on eBay.
Maybe we should start a pda swap/sale section here. (ducking)