No no no no.
If you gonna SLI the 650 1GB and 650 2GB you have no chance for that to work.
This is because Nvidia released a driver than wont support two cards with different RAM.
I also had a chat with Nvidia once when i was so frustrated because of this since i bought a 2GB card and a 4GB card, since i dident know about this driver.
So if you want to SLI, you will need two cards from the same series and have the same amount of RAM.