yeah go with that psu, it will last for ages, i have one and love it to death. i would sleep with it but i would get electricuted.
ANYWHO! yeah that card, thats a pro card. It won't compete with the GTS and is a little worse then the GT at lower res (on par/better then the gt at some higher res games) but you pay 180 for the 3870 and like 3xx for the GTS. So if you can afford it go with the GTS, but think about the 3870 if you want more money for you rather then blowing it all on the build.