Life on charger depends on how you drive it. If you redline it a lot and bounce it off the rev limiter you will strip belts all the time and chargers dont like it. 20k is the ideal for a rebuild on a 65mm toothed pulley.
Would be good to get and will help your power as mentioned all the way through the rev range.
I ran 150bhp with standard bottom end, standard head, Full blend charger (my r1 jabba one gave more boost by 3 psi) 65mm toothed pulley, custom ally intercooler (only one ever made, helped psi increase by 2-3), de-wedged tb, gt inlet and full stainless exhaust system and G60 injectors. My boost pressure was around 18psi then after all the work i had done by boost pressure is 12 which was expected.
I think a remap with my 1st engine would of got maybe 160bhp at a push.