Originally Posted by Z&I

Check out Gates Serpentine High Performance Belts...

"Gates Serpentine Belt-racing Micro-v High Performance V-ribbed Belt "

Their belt design has a shallower rib so it doesn't bottom out on the valley of the pulley [substantially minimizing/eliminating belt slip at that point] but rides on the side walls of the V for more efficient belt/pulley contact surface

By the way ... real nice install :-)

http://www.gatesracing.com/

I think they are available in a number of lengths and # of ribs, but you'll have to contact them via their on-line 'Contact Us' form to find out for you application.

You can always [carefully] trim down to the max # ribs your pulley is designed for with a sharp box cutter.
You've gone this far - that extra rib just might do you righteous.