Think of this like a multi-speed bicycle. A bigger ring up front and a smaller gear out back means you go faster, but it takes more power to push the gear.
The crank pulley is like the big ring on the bike. A smaller pulley means the fan turns more slowly. A larger pulley means it turns faster.
The fan/alternator pulley is like the gears in the cassette on the bicycle's rear wheel. A smaller pulley means the fan spins faster, a bigger one means it turns more slowly.
The only way to overdrive the VW fan is to put a stock diameter pulley on the crank, and the smaller 356 fan pulley on the alternator. I wouldn't do this without a welded and balanced fan. Even then, I wouldn't spin my engine over 6500 RPM or so.
Most people want no more fan speed than they absolutely need. Spinning the fan more slowly means there is more power available for motive power. That's why this arrangement is called a "power pulley". There are many different combinations to play with.