... NEVER PARTITION A PERFORMANCE INSTALL ...
Obviously I'm not that experienced

Nick & Cameron: are you saying that it's better to have the FS9 dir on the same drive as the OS?
I don't even have it installed on the same physical drive. I have two SATA drives (300 & 120) and divided them into several partitions; C=OS, D=Apps, E=Docs, F=Music, G=Non FS Games, H=Films
On the other drive I have I=Vista and J=FS9
There's some additional future space left in the K drive ... which I hardly ever use, exept for maybe storing some temporary work ...
My FS9 library is on a 120 GB mobile HDD. On that I store everything I download for FS9.
I'm pretty happy with this set up and am not very likely to change it, unless you say I can get a big increase in FS9 speed/sharpness if I alter my setup ... after your tips in the
"AA on the card and in the Sim?" I've locked the sim at 24 FPS and it seems pretty happy with that

The sharpness of ground textures could be better and load faster but I'm OK with it ... what would you advise in this situation?
I'm also leaning heavily towards the FS-GS Service ... but need to get a headset for that first ;)