If u dont/ rarely do any video editing, the get the E8400(Well the E8500 wil be better...can easily overclock little higher)
But if apart from gaming, if u are into video editng, etc...then going quad makes sense...But it would be better if u get the Q9550...around $50 more but is worth the investment...it has double the cache and can also overclock nicely...
I would look to the Q9400 myself. First, an increasing number of games are being made that will work better with a quad than a dual core. Second, a Q9400 can be clocked higher than 3.2ghz. I've seen quite a fair number up around 3.6ghz when used with good heatsinks. Third, as time goes on, there will be ever more games that will work better with a quad, or even demand a quad if you want good frame rates. I should state that I was very hesitant when buying my first quad, wondering if i would ever need it. Now I have three computers using quads and only one left that uses a dual core. When Win7 gets released, that last dual core will be upgraded to a quad core. That's how happy I am with quad core CPUs. Oh yes, I agree with gkay09 that spending the extra $50 on a Q9550 is well worth the extra dollars.
As to the Corsair620wt PSU, it should handle the single graphics card that you list (Palit 4870 1gb) with ease. But if you plan to ever use two cards, I'd advise looking to a 750wt PSU at minimum. Many of the new cards are very power hungry. If a person wants 2 gig or more in the graphics cards, those cards must be properly fed.