7870 crossfire would completely own 560 Ti SLI. Not only is 7870 this much faster, but it also scales better in dual-GPU configs. And yeah it'd use less power (about 130W vs 170W per card).
Are you looking to upgrade? Your X750 should handle 560 Ti SLI just fine even with overclocking, and 7870 CF isn't big enough of an upgrade IMO to justify the cost, even though it's faster
I know it would not be much faster. But it should be much much quieter. My 560TI's get pretty darn loud while gaming with BF3. The powercolor 7870 pcs+ looks to be very very quiet.
My top card gets to 90 degrees bottom card about 75 degrees. This is in a Fractal R3 with 3 120MM fans and good airflow. The problem is my Evga SLI board the PCIe slots are right next to each other. So my cards have like 1 mm space between them. And I am gaming at 2560x1440 so my system certainly gets pushed alot while gaming. I did re apply thermal paster MX4 on the 560's as well..