4850 runs hot yes, but nothing extreme. All you have to do is use something like RivaTuner to crank the fan up a bit
The cries were made about the 3870 but I don't have issues.
On the performance issue:http://enthusiast.hardocp.com/article.html?art=MTUyNCwxLCxoZW50aHVzaWFzdA==
You decide for yourself.
"Let’s start with the VisionTek Radeon HD 4850, because for $199 this thing packs a punch. In Crysis we found the Radeon HD 4850 gave us a gameplay experience that was far better than the GeForce 8800 GT or Radeon HD 3870 X2. We were able to play with higher resolutions and higher in-game settings. In Assassin’s Creed we also found a much better gameplay experience than the GeForce 8800 GT and even the GeForce 9800 GTX. We were able to take the game to 2560x1600 with the Radeon HD 4850! Yes, 2560x1600 gaming on a $199 video card. In Age of Conan we were able to run with Bloom enabled, plus most of the settings at their highest values at 1600x1200. This provided a better experience than the GeForce 8800 GT and Radeon HD 3870 X2 which we had to turn Bloom off."
"The Radeon HD 4850 is the new sub-$200 video card to beat as it provides the best gameplay experience for the money. It provides a better experience than a GeForce 8800 GT and a GeForce 9800 GTX and is on par with GTX 260 while being less expensive."