There is no limit to the speed that the CUSL2 can support, apart from what Intel manufactures. The CUSL2 can indeed support processors well in excess of 933MHz....that processor was listed on ASUS' page simply because it was the fastest readily available processor from Intel at the time.
There are a lot of people on this board who are quite happily running their systems well in excess of 1GHz.
Multiplier is not a factor since it is locked....the only thing is FSB. The CUSL2 and CUSL2-C will support all Coppermine processors up to whatever Intel decides to produce, but it will not support the 200MHz FSB Pentium III Tualatin processors coming up.
All current i815(EP) boards will not support the Tualatin either, as it requires the new B-stepping of the i815 (G)MCH.