If you already have the FMF, that would be better than the Pro Circuit, but if you dont have either, the extra $75 that the CT mid range MX would cost, would be well worth it.
The CT mid range MX, could go along with cylinder porting from bottom end to kinda the upper mid range levels, but will fall off real quick the high the rpms you try to make it go.
The ESR TRX 5 regular mount pipe, can work with the same porting levels, but will have just a slight less bottom end pull than the CT, but it will pull in the high rpms a bit more. Kind of a trade off on both ends of the rpm range on the TRX 5 pipe. Most riders, can hardly tell the difference in the bottom end pull of the TRX 5 pipe compaired to the CT mid range.
If you would want a custom made pipe, check with BDT or LED, Kenny at BDT or Arlan at LED can build a fantastic looking & performing pipe for the 250R or most any 2 stroke out there.