FWIW, there's a very comprehensive guide to setting up FSX, and especially your FSX.cfg, here written by the AVSIM Hardware and Operating Systems Forums Manager - probably the #1 or #2 FSX guru out there - here:
http://forum.avsim.net/fsx_guide.pdf. While aimed at setting up FSX to
PROPERLY run under DX10, it also covers general FSX and system settings. Some of it is somewhat technical, but if taken a section at a time if your are willing to take some time to find what works in your particular situation, it can do wonders for your FSX experience. (It contains a good explanation of the fiber_frame_time_fraction=xxx setting, which
is still relevant, and I quote:
"FFTF is an addition to the cfg file, and determines the fraction of the CPU time given to the scenery loader in relation to the time spent rendering. Frame rate will improve as this number is reduced toward 0, however, if run at 0, the CPU has progressively less, or no time to load textures as memory load increases and frame rates drop. The faster the CPU, the lower this number can be, because a lesser fraction of the CPU clock time is required to successfully load that scenery.
Much like BP=0, (Buffer Pools) this tweak is dependent on the balance of the system, and so expecting that lowering the FFTF will always result in a frame rate increase is somewhat of a misconception. Default is 0.33. The lower the number, the better the FPS, but this may also result in ground textures blurring, with loss of autogen. Good settings – start at 0.2 and lower it from there. Experimenting is the key here."
BTW, running FSX under DX10 is the biggest thing happening within the hardcore FSX community right now and a breakthrough application for implementing it is about to be released as soon as beta testing is finished.
http://forum.avsim.net/forum/569-dx-10-discussions-hints-and-help/Setting up my system to run under DX10 by following the guide made a world of difference to my whole FSX experience, and the speed and visual differences have been tremendous. However, it isn't something you can play with for just an afternoon and expect optimum results. It takes time and patience, but the results are stunning.