14.8V 4S LiPo isn't a bad thing compared to a 12 Cell NiMH Pack (weighs more and less run time)

and top speed depends on the gear setup to,besides watching for overheating because of the wrong gear setup

you can slap 2 14.8V 4S LiPo's with good Mah and get longer stronger run times
with the sweet spot of a gear setup
so yes well worth it
just watch out for the draining of a lipo can't go under 3.3 volts and hot is a bad thing
whereas a NiMh can (uses no memory and heat don't harm at draining times) and can be charged at anytime
EXAMPLE; you don't remember if you ran them dead or half full
so recharging them anywhere in that state won't harm them...

and yes lipo in the end costs more..but has better current drain..
it's kind of like fine tuning the motor once you go lipo...lol