is there any difference in performance between the older front upper arms and the new style ones?
yes there is. The new style upper arms are not as wide and are moved more forward toward the tower. They take the caster out of the front knuckles and make them stand more straight up supposedly making the steering alot more aggressive. The old style arms make the knuckles laid back alot. I have these new arms on my RTR ZX1.5R with the crappy RTR ackerman plate and the thing turns which I did not expect. The same ackerman plate with the old style upper arms and the buggy pushes like crazy.