yeah u can buy 48tooth sprokets.
anywho, really the gearing is gonna depend on where u live, and what the traffic is like.
for example in SF its stop and go hills, a 48 on a stock moby is a death trap, a stock moby can't even hang on many greenways. cars will run u down as u try to accelerate from a light.
i don't even run a 48 on my 50+ bike due to the fact that i want the most acceleration possable, if it means i top out low 50's even with all that power then so be it, at least i can blast cars off the line.
if u ride over long distances with little or no stopping or many hills that will really slow you down then yeah go to the 48 or even a 44 (used to run the stock 40tl gear wen i got a variator, u get great gas milage)
the stock unit variator will fully function with these gears.
don't get a performance variator, unless u don't want to ever stop cuz they have no idle clutch functions and the ones that do have no starter clutch functions.
if u want to tune your variator, i'd recomend the mallossi vario plus its a replacement of the moving variator plate that comes with 6 rollor slots and 3 sets of different weighted rollers, u can't mix and match them but u can put only less than 6 in since the pattern is symetrical..yatta yatta...if u get one u can figure it all out.
they are $66 at treats hq
the bad thing is that u have to remove and rebuild the variator everytime u want to adjust the weights.
or u can do somthing crazy like wari will probably do and build the perfect variator from scratch.