AJ,
You know your keyboards inside and out. Bring what YOU think is appropriate with the Roland's.
As for myself, I played the G-70 Version 1 for a couple of days when they first came out. I liked it, but it was a bit too contemporary for what I do. Roland told me Version 3 (the newest) was a "huge" improvement.
I haven't played the E-80 at all.
The S900 and the Korg I could live without.
I wouldn't mind either Roland if YOU think they are similar though I'm inclined towards the E-80 if you have it.
Also...this is a rare chance to see all these keyboards together. Can you consider starting earlier in the morning? I'd like to spend some time on each one.
BTW...I'd be happy with a Big Mac!
Lucky