Edit: Decided to go with a Corsair PSU due to its great reputation as a quality PSU manufacturer...Even though I'm dishing out $30 more . Guess it's better than buying two PSUs due to one going DOA, right?
PSU: take it up to at least a 500w. 550-600 if you want to be safe.
Case: looks far to short to me... i think u will have problems fitting that.
as meodowla said... go for a card with good cooling. HIS IceQ i have heard good things about... also the Pait sonic edition has good cooling (it has 2 fans + heatpipes so its loud but it depends whether u would rather a cooler or a quieter card)
Everyone above this post is just buying into the Manufacturers scare mongering. That PSU will run a HD4850 standing on its head. End of subject. I know of at least two people who are running 4870's on that PSU and have been since launch with no worries at all. Personally i would run the 4850 but not the 4870 but only because i dont like making up PCIE connectors from the spare molex connectors with the available adaptor. If your motherboard is full size then the card will come up just short of the end of the board, my cousins does anyway
I would go for the HIS card as i have had several in the past and am very happy with the build quality having never had an issue with one. The ICEQ version will help with any heat worries as they exhaust the heat out the back of the case but to be honest. Yes the cards run hot but its not an issue they are made to handle it.
You are spot on with your appraisal of the PSU being infact overpowered for the card and while some people will moan (why post if you already decided). There is nothing wrong in my book with checking. Some times you just want someone to say you are right even if your sure, until you have actually done it there is still this little nagging doubt. Right ??