2x 5750's 1GB crossfire vs one 750(non Ti) 1GB?

Solution
When you crossfire the VRAM does not add up so you would stay at 1GB of VRAM vs the 1GB of the 750.

For single GPU performance we have this
http://gpu.userbenchmark.com/Compare/AMD-HD-5750-vs-Nvidia-GTX-750/m7753vs3162

No contest, 750 wins hand down. When you Crossfire you will get about a 40% improvement which is still not enough to catch up to the 750.

Last, not all games will run or work well with dual GPU's, it can be a real hassle.

Winner: GTX 750-1GB
When you crossfire the VRAM does not add up so you would stay at 1GB of VRAM vs the 1GB of the 750.

For single GPU performance we have this
http://gpu.userbenchmark.com/Compare/AMD-HD-5750-vs-Nvidia-GTX-750/m7753vs3162

No contest, 750 wins hand down. When you Crossfire you will get about a 40% improvement which is still not enough to catch up to the 750.

Last, not all games will run or work well with dual GPU's, it can be a real hassle.

Winner: GTX 750-1GB
 
Solution