3 GTX560 TI VS 1 GTX670 I7-3770K

Okay, first off I like to say thanks for all the help this site has given me. Now here is my question, I recently put together a Asus P8Z77 WS with the above CPU and 16GB of Corsair Dominator Platinums 1866 with a Force 3 SSD 120 GB and I have 2 GTX560 TI factory overclocked at 900MHz and the H100 for cooling. I purchased the GPU`s last year and just my luck, the 600 series came out with even more monitor support than just the 3 monitor setup I have now @ 6000X1080. Now I can run my 50" plasma at the same time if I go with the 670. With that thought aside, should I just go with another GTX560 TI? Would I benifit in benchmarking with those three or would I get better performance with the 670 @ 4gb of ddr5. With the 1155 socket I chose, I`m not getting the X16 speed anyway`s, so would just a single more powerful gpu like the 670 be the better choice? I love gaming, but honestly I do more CAD/CAM software than gaming as between work and school, I don`t really ever have time for gaming. So graphics is a major priority for me and a quadro is well, just way out my range right now.

a single card is always a better solution in my book as sli usually only gives you a marginal increase in performance. you could always leave a 560 in there and set it for physx usage. or sell off the two 560's to help cover the cost of the 670.