Well, I went and gave this a try last night. It seems that this actually boosted my frames and not only that but I don't appear to have any lag or stuttering issues anymore! At first I thought this was just in my head but I have been running Mosport, exclusively, for the last two weeks simply because I have had some amazing races with the AI at 102%.
Anyhow, prior to changing the compression values I would get on the grid with 24 cars (including myself, graphics are set to display 25 cars at all times), graphics absolutely maxxxed out, and would see ~65-70 fps at start with lots of stuttering getting into T1. Once the field spread out I would avg. ~120 fps or so.
Now after the change I got on the grid with the same settings and was seeing ~110-115 fps at start and T1 went absolutely flawless even with dust and what not being kicked up. Mind you both times I was starting in 24th place so I was seeing all cars going into T1. Even watching the replay of my race with the tv camera view produced ZERO lag, not even a micostutter!!! I was so impressed that I played EVO until 3 a.m. this morning and almost overslept for work!!
By the way, this is run on an x6800 @ 4 Ghz, sapphire 4870 1gb @ stock speeds, on a DFI LT x48 (DDR2 version), LG 19" @ 1280x1024.
My Ati tray tools profile setting is:
AA - application controlled (set to 3 in Race07 config)
edge dectection - enabled
Adaptive AA - set as quality, and 3 for sharpness
Aniso - set to 16x and trilinear
texture - high quality
mipmap - high quality
vertical sync - disabled
Aniso optimization - enabled
Trilinear Filter Optimization - -enabled
Cat A.I. - high
Flip queue - 0
all other settings are what they were at default
edit: I forgot I am also running some different "dll" file found here ( I have been using this since it's release last year): http://www.nogripracing.com/details.php?filenr=14811