Damn you guys really need to swap a 2t. Id be mad if thats all I got after that much work.
Is there no aftermarket gears for the 4t? Is it a GY6 clone?
I would always upjet anytime the air flow volume has increased. If not later you will find failing rings or worse a melting piston under the wrong conditions. This rule goes for any 4 stroke air cooled engine, if you change the air box to let more air in, pilot must be changed,if no pilot then needle clip raised, exhaust only is main jet raise since max rpm power should be more it needs more fuel to maintain that rpm without excessive heat, if exhaust and airbox replaced, pilot and main jet must be stepped up. Its just my 2 cents with 18 years of motorcycling building and tuning, modding, and riding. Always raise the jetting for the sake of your piston.
As fun as upgrading is, its even more fun still riding your upgraded bike more than a few times. Do it right the first time and save yourself downtime and more money.