A larger crank pulley would spin it FASTER. The compressor pulley will have to make more rotations for each rotation of the larger crank pulley. The whole reason you're increasing the crank pulley diameter is to spin the supercharger faster, correct? It would spin your accessories faster too.
http://www.engineeringtoolbox.com/pu...ds-d_1620.html
I would think the danger is in overspeeding the compressor. Figure out the max speed of the compressor off a spec sheet, and then use the formula to calculate the max speed it would see based on 8000 rpm and the pulley diameters.