Get a 4870 with the better cooling solution
Still toasty. 97C at 98% load and with fan running at 70% speed. http://en.expreview.com/2008/06/24/first-review-hd-4870-and-hd-4850/6/
People blame it on the driver, but that's just an excuse. It's still a combination of gpu that puts out more heat and lighter stock heatsink, even on the dual slot version. That heatsink is physically lighter than the stock dual slot heatsink on, say, a g92 8800gts. Not all stock dual slot coolers are equal.
It should run ok at those high temperatures, since gpu can tolerate higher temperature than cpu. But if you're still not comfortable, aftermarket cooler is the way to go.