2. You might, i would definitely get a better PSU. Even if you don't have problems, it's always better because you should never skimp on a PSU, and it will leave you open to future upgrades.
3. Who cares? They are both terrible compared to the 8800 GT or the 8800 GTS 512 (G92). Your crysis framerates would go up dramatically if you used the EVGA step-up program to go to either one of those cards.
I will be playing at either 1280x1024 or 1024x768, depending on settings.
I know the 8800 GS is a weaker card, and that it probably does not fit a "Crysis" build with a quad-core, but I got a deal on the Q6600: $135 brand new. In addition, I am not what you would call a "heavy gamer." Four cores are great for multitasking, and the 8800 GS offers excellent price/performance (especially considering how heavily it can be overclocked - then it performs on par with an 8800 GT).
I am a bit of a cheapskate when it comes to my hardware right now; I will probably grab an Earthwatts 380w or a Corsair 450 VX eventually, but as long as my PSU can function I will be fine (I won't be overclocking the card until then).
I have been reading that people play a mixture of high/medium settings @ 1280x1024 without AA and pull down 30-40 FPS consistently with this card. It is supposed to perform on par/better than a G80 GTS at 1280x1024 or lower, and I am happy with that.
Your 300W are working at around 250-290W right now, so..a little too tight ,the room you got there mate.
Where do I got the feeling that your psu is something you have kept from your last system.
How old is it? Don't forget to count the components degradation if it is too old, specially if it is a cheap psu.
I think it would be very wise if you bought a new one, if you still love your new system.