You're right, the original drive was good for the designed purpose.
I'm not sure if higher RPM will overload it since it automatically increases belt tension, but higher boost pressure is going to need more friction surface at some point.
If you have a width problem, just going to larger diameter on both pulleys helps since the actual driving surface isn't the belt width and profile, but a (more or less) fixed percentage of the circumference. A 6" pulley driving a 9" pulley at 1.5:1 may have 40% belt wrap on the 6" and 55% on the 9", or 23" length.
If both sizes were increased in proportion to 8" and 12" (same ratio), the belt contact goes up by 33%.
Re-positioning the tensioner pulley to the outside, and closer to the centerline also increases belt wrap (although flexing the belts more increases heat and reduces life).
