I think I have to add some more in deep information why the pulleys are more than worth the money.
I'm using the Macht Schnell kit and compared to the BMW stock ones it's one of the solutions which you need to keep your power steering oil from boiling!
Stock BMW ratio to the power steering pump is ~1.11
Macht Schnell is ~0.89
What does that mean? Easy math. When your engine is at 8000rpm the power steering pump is not at ~8900rpm but at ~7120rpm.
That's ~25% less rpms on the power steering pump!
Why is that so important?
Well - everybody who tracks his car knows about the boiling oil.
As some know I'm driving a lot on the Nordschleife - problem of the track. Due to some jumps and many corners it adds additional load on the power steering system.
Step 1) With the Macht Schnell pulleys I was able to do some laps without a boiling oil.
Step 2) To get it really rock solid even during hot sunny days you'll need an additional power steering cooler.
If you look at the BMW GT4 power steering cooler you'll see that it's much larger than the stock e9* M3 cooler. They didn't change it for the racecar without reasons.
Here's my solution. This cooler here is added in a row to the stock one.