Hi Nick,
Your best bet would be to post your questions on the Roland arranger site.
http://www.roland-arranger.com/smf/index.php As far as I know, the keybeds are different between the E-80 and G-70 (not just the number of keys) although they both have aftertouch, and, the E-80's latest OS upgrade included an MP3 player.
I played them both, and I liked the E-80 more than the G-70, although both have a bender/lever that I didn't like much, preferring separate pitch/mod wheels myself.
You should also consider parts availability in the future, as these instruments have been out a while, although both are excellent and well made arrangers.
Ian
[This message has been edited by ianmcnll (edited 11-26-2010).]