Sli questions with 8800GTS 640MB

No u cant
http://www.tomshardware.co.uk/foru [...] 0gts-640mb

Do the cards have to be same model?
I answer it with an example:
You have a NVIDIA Geforce 7800GTX 256, and you want to add another card , the second card has to be 7800GTX exactly

I ordered two G92 8800GTSs from newegg and than cancelled. I got scared. A little less than 700$ with MIR. I saw on ebay that the old 8800GTS are selling at around 240$.

...500$ for SLI G92 ?
Or should I go with 8800GT?
Or should I wait for the new high end card to come in?

I never knew to cancel newegg orders. I would always just cover my eyes and pretend like I hit the "confirm order" button by accident and than say "oh well". 700$ is a lot of money though.

Also, if I were to buy two 8800GT should I get the 512MB or 256MB. 256 seems kinda small these days and I like to play at 1680 x 1050. It is 80$ for the difference times 2 for SLI. How can they charge 80$ for 256MB vram