I have just switched to the RRR for the Foam Touring class as it is a much more aggresive car, but if you are running Rubber or want an easy car to drive fast then the FW05RR is the car.
Shaft cars lack in friction drag, so they launch out of a corner faster even with a taller gearing, but they don't slow when you come off power so they can over run corners easier.
Which do I prefer?
RRR is quicker and you can hit the power harder and earlier in a corner but you have to be 100% or you'll loose the rear.
FW05RR is faster and very much easier to drive with loads of rear end grip, but it lacks that much needed front end bite when powering out of a corner.
RRR is needed to run with the 710's and MTX3's in the Foam Touring class as the FW05's lines are wrong, but in the slower paced Sports class nothing can touch the FW05, be it R/RR/S or T version, they show everything else up.