^^ thought so.
However, if a cheap, low-power G4 can get anywhere near a low-end GPU in terms of hash-rate...
NO, not ever. Not even close.
I'm not going to bother with the math, but architecturally the SSE2/3 instructions are vastly superior to whatever the last-generation Altivec instructions were. A G4 wouldn't even be half as fast as a modern Intel CPU.