You may want the larger power supply anyway. And here are the reasons:
 
1) The SR-2 is very picky about it's power. At first boot it is known to droop many power supplies. I've seen it with a PP&C 750 (60 amps), and Apevia 850 (says 70 amps, I don't think so), a thermal take 850, ect. While the best supply I've used with it has been the Seasonic M12D. Does a nice clean 80 amps, and with the dc/dc conversion the 5v/3.3v rails stay very clean. The single Seaonic did better than the above even when they were in dual supply configuration. Note the Seasonic was still a "850 watt" supply, but it put out 840w on the 12v rail. 
 
2) Power supplies are more efficient when they are not running at max output. If you use the eXtreme Power Supply Calculator it says about 527w for your config at stock voltages. I'd add say real life will be closer to 650 watts. That puts your 750 watt supply under a 86% load, and little room to overclock or go sli.
 
3) When you buy the larger power supply you can get a gold rated one with all the power connectors you need. They can be up to 95% efficient at 230 volts, and will allow capacity for overclocking your x5650 chips, to say 4ghz, and to add a second card for sli, plus expand your raid array.
 
 
 
 
 

Hi, thanks for the reply
 
now I have a Giga GA-EX58-UD5 with a same configuration (except, obiously, the SR2 and the second xeon),
 
test with gpu_burn (a linux GPU test with CUDA) and the same time encoding x265 video with a rageload configuration. the PSU weathered perfect (yes , i am a linux user), y don't know if with a second xeon (TDP 95W) and the mobo consumition break the PSU.
 
looking in the forum/google i found a pair of users with a single Corsair AX850 (because have a 2x 8p ATX output) with, more or less, same configuration.
 
750W baybe is a little, but with 850W with a GOOD PSU (like corsair) i think is enough.
 
first need a mod my Thermaltake V8000 Armor (LOL) to fit the beast, then we'll see
 
greetings and thanks
 
 

I work with a seasonic x1250 . Why so You Must have 2 8pin ,1 6pin for pcie And min 2 6/8pin for Grafik!

Myself have 2 gtx 660ti And 2 l5520@blck 210 !

The power are by 905Watt AT Full Load so you get a Little More power for Future .