Sorted it out.
Overclocking the 5850 is easily attained with the AMD GPU Tool and MSI afterburner together.
AMD GPU Tool for overclocking the Core and Mem
MSI Afterburner for ramping up the voltage and fan speeds.
It's a little clunky as you need both the software, Msi's AB can't change clock speeds and AMD GPU tool can't change fan speeds.(can change voltage but maxes out at 1.088) MSI's AB also allows you to set up an personalized auto fan speed profile, so your fan will adjust it's speeds automatically but according to your parameters. And the profiles can be saved, even to hotkeys. Makes OC'ing the card a dream actually.
Of course a BIOS update to your card will allow it to be overclocked entirely with MSI's Afterburner software alone. There a risks involved with this, such as bricking your card and IMHO it's neither really worth the risk, nor the grey hairs.
These two programs will easily OC the Radeon 5850 to >950 Core, 1150 Mem.
I'm running stably at Core 960, 1150 Mem and 1187 Mv.
Pretty sweet i'd say.
This is a pretty good link.
Links to all the apps you need are on that page.
Other than that, guru.3d is hosting the MSI AB forums now if i'm not mistaken, good place to look for info.
Happy OC'ing everyone.
Thanks & cheers.