In almost all situations, you will lose no top end with a 23t. The sled just won't pull the gear in most if not all conditions. You can change out the bottom gear on reverse models, just make sure you order the appropriate part# for reverse model sleds. They cost more. About 110. 25 or so for the top cog. 22/38 would work fine, but you'll need to spring for a chain. If you go 23/39, you can use your stock chain. You also get a better angle between the tensioner and the bottom gear using a 39t. This setup works great for me and is a cheap way to add trail performance.