You should stress test it when you get the new power supply in. I've got a PCP&C silencer 610W running my rig (about 2 years and counting). The 5 year warranty is also quite nice
Oh, and 750W is PLENTY. You can run at lot of hardware off of 300W. Check it at the wall if you're curious, or put your hardware in here:
http://extreme.outervision.com/psucalculatorlite.jsp
I used to be a fan of a program called Prime95, but, due to simplicity and more capabilities, I like using OCCT now. Here's the link:
http://www.ocbase.com/perestroika_en/index.php?Download
Basically, run the stress test for a couple of hours, watch the temperatures (don't let your processor get too hot - maybe 65C max), and check for errors throughout the process. The test will stop if it detects an error. There is also a PSU test that loads up both the processor and graphics card (if it's new enough) to maximize the load on the power supply.