Did some poking around some Cooper S forums and 15%, 17% and 19% seem to be the most popular pulley reduction choices. There seem to be dramatic differences between the three, performance-, heat- and whine-wise.

Given the obvious differences in engines, how much reduction do you predict we'll be seeing for the 3.0T?

Seems you get about an extra 15 HP on the Cooper S with a 15% reduction in pulley size. So that's about 10% over stock HP. Assuming similar gains on the 3.0T that means about 30HP. Not quite turbo chip level increases, but I guess it is still something. Especially if the pulley cost is kept in the sub $200 range.

As you said though I wonder how much extra whine, heat, and reduced lifespan a different pulley will cause.