FXR is going to be slower - if you take a car and add 4WD, you add extra weight via diffs etc, and those extra spinning things means more transmission loss and less power to the wheels. The advantage is you can get the power down earlier - however with "only" 500 HP from a laggy turbo and a smooth slick surface, that doesn't outweigh the disadvantage for pure speed.
The advantage is you can be much more consistent in an FXR - too much throttle in an FZR and you have 250 BHP per wheel pushing you anywhere but straight, too much throttle in an FXR and you have 125 BHP per wheel at the back doing the same, but 125 BHP at the front pulling you forward, counteracting it. Similarly the FXR is also slightly easier on tyres because theres less power willing to burn rubber to each individual wheel.
You can't compare that in all out times the FXR is slower... because it should be. On a long race level they should be closer, but still the FXR should be slower because it's easier and more consistent. What'd be the point in getting in an FZR and running the risk of spinning when you can run in an FXR at the same pace with reduced risk?
If I was going to drive an endurance race i'd pick an FXR for the first few goes - because while I'm not exactly shit the 0.5 seconds I might lose one lap could be more than made up by the 20 seconds I lose spinning off into a wall and the subsequent 3 minute lap I make limping back to the pits. If I got consistency down then it's time to add more risk and try to get that extra 0.5 seconds.
The point of a class is that the cars are different - each car SHOULD have advantages and disadvantages. You can't chose the easy option and the bitch because it's hard to win all the time.
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