Why not go with PAYE/IBR and choose the plan that offers the lowest monthly payment? Then you can control where your extra payments go if your loans are divided up into "accounts" so that you can pay off more of the principal. This is assuming that your loans are divided into accounts (obviously), you're able to allocate paying off a single account at a time and the monthly payment being dispersed across all loan accounts, which I don't know if that's the case or not.