Keeping in mind that you always need a load on the clutches, you always need to make sure you always have gear to keep a load on. A stock Apex with 150 hp will not pull a 24 gear nor will it pull a 23 top gear. A stock Apex with 24 top gear will radar on ice about 110-115 true mph. In actuality if it had the power to fully shift the clutches, it would go a true 130-132 mph. A 23 top gear would be gearing down a bit and bring top speed a true 124ish mph. Again, tuff to hit with a stock 150 hp motor. The benefit of gearing down allows for more mechanical advantage in clutches to shift farther thus more top speed. Also shift quicker for better bottom end. The 23 top gear won’t do any magic, just easier to work with since 24 gear is very tall for 150 hp. There are a few good clutch setups that work great when mixed with the 23 top gear. If you only change the gear, just check your peak RPMS and make sure your still in the sweet spot. I wouldn't get into cutting or shaving the clutches for getting a farther shift, not easy to do and most of the time your asking for trouble.
Dan