We run Rotax Junior. Best I can tell from what Rotax has published is that the only items that will provide a performance advantage with the new upgrades is the carb and ignition system. The carb has been redesigned to improve bottom end power/throttle response and minimize the effects of environmental changes so that the carb is much easier to tune. The new ignition system improves the power band and rpm in the 12K to 14K range. These were two issues that many customers have always bitched about…so Rotax fixed it! For the price of a cheap axle and sticker kit ($500) the playing field will better equalized.
The other upgrades are designed to improve durability only.