I reckon that the cars are getting to or have already got to the point where it comes down to car preperation and driver skill (and that anoying thing called luck). Personally Id get the Mugen only because in my country Kyoshos are very hard to get parts for. It would be a battle between the MRX-4 and the Evolva, I wouldn't get a Serpent every race ive seen with one in it craps out like the 2004 winternats dvd Mugen wins and all the Serpents craped out.
The 1/8th are so fun to drive its just like F1 but in r/c cars (i know thats been said elsewere) well thats what i think any way of the whole 1/8th scale stuff.
Chris