Big Difference
OK after some research i decided it was relatively safe to overclock the late 2009 imacs mobility 4850 hd card. Here is a post from someone who has the best solution for getting the imac to perform better and hit the higher benchmarks.
"As far as overclocking the mobility 4850 goes, use msi afterburner. In order to get msi afterburner to overclock mobility cards, you need to edit "allow unofficial overclocking" line in msi afterburner's config.txt file. Just open it up in notepad and find the "allow unofficial overclocking' line, and change the 0 to a 1, then save the file with its original name.
You can push the mobility 4850 to pretty high speeds, because the 27 inch iMac has rather good cooling when you crank the fan speeds up. If you crank the odd fan up to max, you can get away with desktop 4850's clock speeds (625mhz core and 990mhz vram) An overclocked mobility 4850 with those clocks will perform exactly like a desktop 4850.
With the odd fan maxed, you won't see your gpu's temp rise above 70c. To set the odd fan to max rpm, rev it up with smc fan control on osx, then restart the computer (not shut down) and go into windows."
it works.. my low resolution scores went from around 2700 to closer to 3100-3200. u just HAVE to keep the ODD fan at least 50%. I would suggest 75% but its a little loud.
