Graphics card for AE?

Hi,

Some advice on graphics cards, please.

I need to buy a new PC quickly, so don’t have time to save more money. (My AE [CS5] projects are small and modest, not monsters with 1000s of layers with 100s of effects.)

I know graphics cards play a big part in gaming, but how important are they for video production?

Here are my options for a six core, 8gb RAM PC that I can just afford:

ATI 5450

ATI 6450

GT610

Can I get away with a cheap card or will my system really suffer?

If these cheap cards would be a nightmare, would a 6770 or GT640 make a vast improvement?

Like I said, budget and time are both big problems!

Thanks for any help,

Steve