Hmm, just don't know whether I'm kicking a dead horse here. It's an old thread. But really, I've been hacking on CLN/GiNaC support for ARM lately and they seems to fit well into quite old ARM computers. Many PDAs are running on such things. So, the portability is there and the machines are getting faster than what we see here:
timings snipped
From my own testing with giac/xcas on skiffcluster5 (Compaq cluster), it seems that you can expect about the speed of a Pentium 60Mhz (well I hope the speed of skiffcluster5 is about the same as the speed of an iPAQ). The problem is more size (display size and flash ROM size) than speed. Some examples (without optimization flag for compilation)
factor PIII-500 skiffcluster5 HP49 x^10-1 too fast 0.1s 17.0s x^100-1 0.12s 1.82s not tested x^202+x^101+1 4.07s 52.07s