Basically for a Vmax there is only stage 1 and stage 7. Since your using slipons, the best hp gains will be from jetting DOWN....going from the stock 152.5's, to 150's....or even 147.5's.
To be able to really use a stage 1 or higher, it requires using an aftermarket exhaust.
The main HP RESTRICTION in the Vmax, is the stock head pipes.