I got my 166mhz from GBAX.  It ran fine at 166mhz but no higher. 
So I opened it and modded it myself.  The motherboard hadn't been touched , so I assume mine was a 166mhz one out of the box.
Well anyway, mine goes to 200mhz now, but it did take me 3 different resistor combinations before I found the right combination to get it that high.