medusa 2000kv 60mm motor

hi guys. i am a little disappointed with my medusa motor. the temperatures are great it is alot cooler than my 9xl but the speed isn't really that great if i am honest. compared to the 9xl it seems about 5 mph slower.
i have geared it up to 16/stock losi spur but it still doesn't have much top end?
i came into a bit of money so thought i would spend it on a new motor but did i get too lower kv motor on a 14.8v lipo in my 8b? would it be better to run it on 5s instead of 4? the mamba max esc stays super cool (i have a brushless fan on it and a BEC but don't know what caps/ how to wire them) so would it be ok to run on 5s?

thanks richard