I'd stick with the chip you have personally and get an Nforce2 motherboard, they'll do the job at 200 FSB and you can run a decent DDR400 ram in dual channel 1:1 with the CPU instead of single channel like the KT400s. A used NF2 board can be had on the REAL cheap now a days. If you want a new chip just get a mobile, garunteed unlocked and a prime picking as it has to run at low voltage out of the box. I have a Barton 2500 XP-M that always ran well, didn't OC incredibly (2300 or so stable, but at low heat/voltage).
Edit: regardless, your current setting is a decent overclock especially given the equipment you're using, too bad the chip has a locked multiplier.