As it is (I am also looking for an f50 decent sound) there is not a lot one can choose from. I have tried almost all cases, plus the ones mentioned in this thread (the f40 sound as it was previously stated does not suit the f50) probably the most reasonable ones are the FXX (a bit high pitched for the f50) by DoctorG and the TDU sound of the 575M since are both derived from Ferrari V12 Normally Aspirated engines. (The f50 has smaller block, hence the uniquiness of the sound that it makes).
Maybe we can start a poll to see how many members have the f50 installed and see if a sound modder can produce us a nice sound for it!!! :)
Unfortunately the 250GTO Breadvan sound is amazing (and deep) but sounds different from the f50 in low and mid revs (in my opinion).
UPDATE: This is what I am talking about...
If that sound could be converted for TDU -> Happy Days!!