You should be okay for medium range settings- the 5850 is going to be your bottleneck. Have you OC your 2500?
Keep your tree and clutter distances down- might need to pull back view distance to medium to ensure a smooth experience. Blur off, tree shadows and cockpit shadows probably off? Water medium / but I've read that high shadows actually helps fps.
Mfcd res to 512 (not each frame).
Again I'm being conservative. If you had a newer GPu you'd be fine...
To give you some perspective I'm running a 980x at 4.2 with 12GB ram and a 680 GPu and I can't go full bore with the graphics settings.
Go through the GUI manual that's available (there are two manuals) and look through the specifics of each option.
