I started to notice lagging movements that seemed to increase the more i moved my head. Obviously i looked around many forums for a fix, and i think i may of found one (at least it works for me).
I downloaded the freeware bloom mod called ENB Series, and it contained a "how to install" file, and and config file, and a d3d9.dll. After extracting these to my FSX folder, I now have no lag whatsoever. I don't know if this is down to the mod itself, or the d3d9.dll was supposed to be in the FSX folder anyway.
I hope some others try this, and please let me know if it helps

Link to mod: http://artificialanimation.net/downloads/ENB_FS.zip