Considering the Power Supply is the MOST important item in any system .I have no problems Purchasing the best One to get the job done .Instead of buying cheap low end Units that never deliver the proper voltage .I would save my money and get somthing that will handle anything i throw at it.You save money in the long run instead of waist it.
2 slots is no big deal. In fact if you have a high end card now with no open slot below the card that will cause heat problems guaranteed.I NEVER put a PCI card under the AGP reguardless of the cards architecture. I run AIW 9700 Pro
9800 Pro, FX 5950 Ultra all with a slot empty under them.
The ATI cards have heat issues that affect there performance and even cause crashes.I remedy it by leaving the slots open and even upgrading the wimpy fans they put on them. In my opinion ATI cripples there cards with inadiquet cooling . Every High end Nvidia Based card ive used or tested . Has allways addressed the heat factor on there cards.I will be getting the 6800 Ultra soon