Haven't tried overclocking my 4850 yet, but I have put an Arctic Cooling Twin Turbo on it, and even with the fans on low speed, it never gets above 55C peak, so certainly room for an overclock there
Until I get a better monitor the 4850 is doing me well, a 5850 would be nice
$1500 lawyer bill I got yesterday might delay that though haha
For the BIOS version, under the Mainboard tab in CPU-Z there is a BIOS section which should show you the version currently running.
Generally though, if you're happy with your machine, there isn't usually much reason to upgrade the BIOS on the board. Unless you've spotted something in the BIOS releases that you really want. I find it annoying, as I just have to enter all my overclocking values again.