if you put the physics file in the mod folder data/patch - it will automatically insert it for you - name is not important, so long as it ends .3gp
if you have one generic performance file, you can put it in the same folder as the physics file, again so long as it ends .txt
You will need a performance folder if you want track specific performance - you will need a separate gpxset.ini (for gpxpatch) and you will need to swap these into the correct locations.
Hope that helps