Gearing down a PF XL I'm looking for the best way to gear down a Power Function XL.

I need to achieve a very slow output RPM (less than 1-2 RPM). I've tried a 625:1 gear (trough 40:8 gear). Can someone link to a well done gearbox like that? Moreover, how I can make an axle more resistant at high torque (I've tried with brick round 2x2).
The XL motor runs at approximately 220 RPM.  Therefore, the following gearbox from the ELEC 201 class LEGO Design module from Rice should be sufficient: