For better hill climb power fit a stiffer torque spring in the rear pulley. You can buy a pack of 3x comes with a 1000, 1500, 2000, rpm spring. I just got a set last week, fitted the 1000rpm and def felt a difference, extra 5-8mph uphills. Going to try the stiffer 1500 or 2000 rpm in it soon to see how that does, hopefully be even better, once I get it matched in with suitable roller weights.
If you fit a tighter torque spring, in theory, you fit heavier rollers to gain a little more too speed. The torque spring balances out the heavier roller weights by keeping it in a higher gear on the rear pulley longer.
Also stiffer fly springs in the clutch gives better take off speed/acceleration. Again you can buy a pack containing 3x stiffnesses, 1000, 1500,2000 rpm rated. I plan on ordering a pack and trying out 1500 ones with the 2000 torque spring and 7.5g rollers soon. Will either be great or terrible, only one way to find out tho.
You can also fit a race variator too for better acceleration and usually a little more top end.
All of the above are pretty cheap parts and if you fit them yourself it wont cost much to do for some good gains. My agility 50 4t now hits 48mph, even get 52mph on a good day
Hope this helps, oh, and welcome aboard I hope you realised once you start tuning its very hard to stop