Need help on new video card

I recently bought a video card that was a week old of a friend of mine it was the BFG 9800GTX+ 1GB version to replace my 8800GT 512 MB. I bought it to put in a system i build like 1 or 2 years ago or so

System spec:
Intel Core 2 Duo E6420
4 GB DDR2 800
9800GTX+
asus P5B VM SE

I have to question first of all in my game of choice (WOW, yes i know it succked me in nothing i can do) i didnt see much of an improvement at all...in fact in some places im getting worse performance.

Now i see two possible problems that I need everyones help on. First, Could it be my processor bottlenecking the system.
Second, im only running a 430 Watt powersupply for the time being and the card recommends a 475 watt. Now i went to a few Power Supply selectors and it recommended like 400 for my system. But im curious as to the accuracy of those. And if so would a Higher in video card that was being under powered provide the same performance or less in theis circumstance...

Any help would be appreciated. Any other Questions just ask

your 'upgrade' is really not that big of an upgrade per se. As for performance in WoW you aren't going to see drastic improvments at all. As for the downgrades in performance you are seeing well...did you change any of your video settings or are they the same? Whats your res at? Do you play with V-sync and Triple buffering on? Do you play with multisampling turned on? Where were you seeing the slowdowns? Places such as dalaran, IF, etc that are highly populated even some 25 man raids are always going to show slower framerates rather than flying around in low populated areas of outlands/northrends. Overall the 9800gtx+ is just a better version of the card you already had. So most of the performance you got out of your 8800gt are going to be the same in wow with the new card. As for power issues if you weren't getting enough power it usually wouldn't show itself as a slowdown in games. For me it usually shows its ugly head by causing system instability (BSOD's most commonly or apps/games crashing). So my guess is if thats not happening to you your power supply is ok.