That amiga used a 68k? I believe that the newer Texas Instruments calculators use 68k's, and are overclockable throught the same means. The soldering involves removing and replacing a capacitor i believe, which functions as a clock crystal for the calc. I was half-tempted to o/c the Z80 look-alike in my TI-86 via the same method, but I would have had to mess with surface-mount circuitry, and that's something that I don't intend on ever messing with.