FS 2004 more demanding than Prime 95 and SuperPI!

Installed FS 2004 again for the first time on several months. All default scenery untweaked win xp system with zillions of background processes.Start the default flight at KSEA on a Cessna 172. 15-20 fps very erradic and extremely low refresh of mouse and keyboard.All full and all optimizations off on my 6800 ULTRA 4x aa and 8x aniso. After taking off I got frames in 25-35 but my keyboard was still very sluggish to fly with.CPU temp -15 with prime 95 torture test blend it goes down to -16 and SuperPI quite similar. My A64 is at 2,5 gig currently and my mem at 250 Mhz at CAS 2,5-3-2-8.So it looks like I still got some tweaking to do but not to bad at first try. 1600x1200 or 1280x960 hardly made any difference in performance though.Now what are you guys more successful with. having the memory tweaked for large system cache or for programmes? I am a bit weary of the large system cache option since on ATI cards that could give you serious disk corruption having to reformat and everything but haven