I have one EVGA GTX560 card in my machine right now and I understand I MUST match it with another like it but what if I tried to use a GTX560TI would that affect anything or would that be an improvement?,or do I just totally HAVE to match the whole shebang exactly?
you have to get the same gpu, it has to be a gtx 560, not a 560 ti or a 560 se. it should still be an improvement though. but considering a gtx 660 is only 40 bucks more then a gtx 560 it might be worth it to dump the card you have now and go for that. if you still want to sli make sure your motherboard can support it
If you decide to do SLI, be sure your board has PCIe slots that work as x8-x8 or better. If one of the slots is x4 bandwidth, it will drag down the performance. Another drawback with 2 mid range cards in SLI is the possibility of micro-stutter: http://www.tomshardware.com/reviews/radeon-geforce-stut...
Although I cannot attest to this myself, if you run out of VRAM, then the GPU will dump to the RAM of the pc and hence will result in 1-4 fps. There are only a handful of 2012 games that need more than 1GB for the high quality textures so if the OP is not trying to play them, no problem. To be more future ready, 2GB is a reasonable choice.
In regards to the OP, yes they must both be 560s (non ti).
Could you tell us what games, resolution and quality you are aiming for and why you feel you need to upgrade?