Well what kind of an OC are you looking for, 3.2/3.6/4.0ghz?
I'm currently @ 333FSB(3.33ghz) on the 266 strap with every voltage option set to stock except memory and vCORE(vCORE is undervolted too).
4.0Ghz(450FSB) is doable with GTLrefs still on auto, all you really have to manipulate is CPU VID control and NB voltage...
NB voltage = 1.35V (might even require a little less)
CPU VID control = 1.XXX (You'll have to figure out this one on your own not all chips are equal)
every other voltage can be left at stock/auto
Another thing to consider is the DRAM speed, you should select from 333mhz strap @ 450FSB...
Option will look like this:
The higher the strap chosen the looser the sub timings(typically better stability)... you can check that out for yourself by booting into windows @ various straps and opening up memset(found here