Need advice for upgrade

Hello everyone,

my pc ATM looks like this:

Core 2 Q 6600 G0 @2,4GHz O/C'd to 3.0GHz
2x2GB Corsair Dominator 1066MHz
XFX GeForce 8800 GTS 640MB
Asus P5Q mobo

I want to make my pc fully hd capable, so I'll buy a Blu-ray drive, a new PSU and a GPU. Ande here's my question:

I'll need a quite powerful gpu to run 1920x1200 screen (I want to buy samsung T240, if I'm about to make a mistake with this one plz let me know as well ) I've been thinking about GTX 295 (single PCB), I read that its incredibly powerful, and relatively cool'n'quiet, but I wonder if this kind of gpu won't be an overkill for Q6600 and 4GB ram? If rest of the system would set his card back badly, then what else would you suggest (nvidia preferred)? Would I have to upgrade sth else alongside gpu? (not to mention PSU, obv...)

And don't tell me to wait for new releases this winter, I prefer to buy tested and polished products over absolute novelties.

Secondly, what is the highest acceptable temperature for my CPU? After overclocking temp jumps to 66C under load, and I want to run some more tests, but i don't know where the border line is.

I'll be really thankful for helping me with that.