help? have a hitachi 250gb 5400rpm. quiet and fine. but too small. i have an ssd for apps+os (optibay). I want at least a 640gb to make it worth the upgrade. considering 640/750/1tb. preferably 5400rpm to be quiet and not make vibrations. i have quite a bit of store credit at newegg for returning a nonreturnable item (slingbox, didnt work out too well). thanks guys reliability is important too.