OPC 660 upgrades?

I havn't tried this, but I guess that even though you you install a 256 MB stick, the OrangePC will recognize it as only 128 MB.
On the other hand, I bet it's possible to have a 550 MHz K6-2 run at at least 550 MHz. I'm running a 450 K6-2 at 500, so with proper cooling, you might get the 550 to run at 610 (set the multipliers at 5.5 and the bus speed at 111). Or even better, stick a K6-3 450 MHz into the 660, and overclock it to 500 MHz.