Whoops I just realized the max BCK is 9.2Mhz (that's what i get for writing this at 3am), so you could just divide the arduino's clock by some int to get 8, 4, 2mhz whatever. My thought is to try 4 or 2 so that you have enough time for processing samples, e.g. the arduino runs at about 1 MIPS / Mhz so having a few extra instruction cycles could be handy.
with the wavetable synth you mean this: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1227287786 solution, althoug he has it in HEX?
Yes that is wavetable synthesis, but it seems silly to use wavetables for easily rendered waveforms like square/saw/triangle.
Saw - just count up +1 (or down)
Sqr - 1 for half the time, 0 for the other
Tri - count up for half the time, down for the other half
It would be a better use of memory to load up complex waveforms (i think, maybe the arduino can't produce the basic ones in fast enough).