I've been playing with the E3 some more and couldn't resist compiling libspectrum and Fuse for it (from http://fuse-emulator.sourceforge.net/fuse.php).
It runs it at about original speed, however it's going flat-out doing that and increasing the emulation speed above 100% seems to make little difference.
A couple of screen-shots are at:
http://www.whitakernet.com/e3/spectrum_on_e3_1.jpg http://www.whitakernet.com/e3/spectrum_on_e3_2.jpg
I had to make a few simple changes to Fuse to get it to work with the strange resolution framebuffer of the e3. If anyone wants to build Fuse themselves let me know and I'll post the patches here.
All of this is totally pointless, of course, but it bought back memories typing single-keystroke commands using a rubber keyboard!!!