Upgrading, psu, pci-e and price query.

I have a 8600gt 256 and I am wanting to upgrade to a 9800gt 512. I don't understand much about power supplies, with the 12V ratings and everything, though I gather they are important.

This is my current power supply http://www.thermaltakeusa.com/Product.aspx?C=1247&ID=15... with one exceptional inconsistency on that output chart vs what it says on the sticker of the actual unit. Mine says the -12V is 0.3A rather than 0.8A. Not that I know the difference or know if it's at all important. The page prior to this says the PSU has a +12V of 29A which I think would be enough for this card but from what I have read, you can't just add the the +12V together like that (15A,14A) or maybe you can do that, depending on who I am reading  

I'll try to give as much info on the rest of my computer that I can think of. I have a Intel q6600 processor, 4 gigs of ram across 2 DDR2 800 sticks, 1 sata 3.0 hard drive, 3 120mm case fans. I don't know how much of a difference it would make on taking up power, but if it's of any interest my DVD-RW is external with its own power supply. I'm not an expert builder but to my knowledge, everything is roomy, running cool and very stable as is. If anything else I left out, I'd probably know if asked.

My second question, to my understanding a card with PCI-E 2.0 capability will work in my older x16 slot, correct? If so, would it make a big difference in performance?

Third, since I'm not incredibly in the know of historics or upcoming products, what would be a good time to buy between now and Christmas? Will prices drop much more (99 after rebate average) or is there no reason to wait?