4850, 4870, or geforce 9800 gtx?

This is killing me.

Mobo: Gigabyte EO45 - UDEP
CPU: Intel Core 2 Quad Q9550
HDD: WD 320GB SATA
PSU: I'm planning to get a 500w since I dont have money anymore.
Memory: I dont have yet but I think I'm getting a Patriot/Corsair 2gb (2x2) = 4gb with 1066mhz
So its like this.

For the past weeks I've been researching about gfx cards and I would want to get one which I wont have lots of problems with and at the same time, will have nice graphics.

I was supposed to go for the 4870 but I dont want my gfx cards to overheat and have problems like those since I'll be bringing this computer to the Philippines which is a very tropical place (95 degress F). I saw 4850 and tried to compare it to the 9800 gtx, it was both great and I can't decide which one to get. I dont have enough money to go Crossfire or SLi. I need help on choosing a video card so can anyone help?

I'm planning to get a computer case with 3 or two big fans to keep it well ventilated, a big mid tower would do perhaps?

I'm also considering these cards performing with a 500w PSU. I'm not planning to get anything more than 500w, I have a tight tight tight budget atm.

HELP please! And if possible, please tell me where to buy it and what website thanks!

i've had both the 4850 512 meg and the 4870 1gb. Both are decent cards, the 4870 is a very nice card and i did not have any troubles at all with heat and i kept it OC'd 100% of the time.

Brand i has was Sapphire.

Hope this helps

Ps. For what it's worth, i would vote against the 9800gtx, the 4xxx series cards are newer/better in my experience

I've got a 4870 with a Q9550 processor and I couldn't be happier with it. No problems with overheating/power, and with a single card 500W should be just fine for you. Don't get the 4850, the tradeoff to the xx50 models from the xx70 is usually going to be noticeable.