GTX460, or 5850.
I would say 460 because of the better price/performance ratio. I know you said you have had troubles with nvidia heat in the past, but that isn't nvidias fault.
If you look at the different nvidia cards, they all have different cooling sollutions. That is because the different manufacturers stick their own cooling sollution on there, so it is the company that distributed the card's fault, not nVidias.
For instance, I had an 8600GT silent cooling, and because it was passive and at the time I didn't have the greatest airflow, my card was overheating. I spent ~£20 on a new HSF, temps dropped to normal levels. It was because Asus had decided to put a POS cooling sollution on there, not nVidia's chip causeing the problem
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130564
$10 more expensive than the 5830, but outperforms it and uses less power. Also EVGA have very very good warranty and (I have heard this, I know they do it but not exactly how it works or what it is called) a system where you can part trade in a component to get a more up to date one, but I am not sure if that is only direct from them, or only on certain products, or only certin people are eligable or what. Someone with mor experience with EVGA would be able to tell you