Lots of variables !! Any mods to engine? Size of tear tires?
In the end only you can answer that question, you'll have to experiment to find out what is best. More power out of corners or speed for jumps.
What gearing do you have now?
Be aware that it's recommended to change both sprockets and chain as a set. However , if you had a new chain and several sprockets you can change back and forth without problems.
FYI, Next time only start one thread per topic. Having three won't get you a faster answer.