After much research and advice I decided to go with the 1" Flame Retardant Polypropylene Split Wire Loom (I got 100' - I'll probably use some in my house too).  It's got the widest operating range, it's flame retardant and it's even more flexible than nylon (I've got some tight curves, so that will help).

I figure that if I have some electrical short that causes a flame in the wire bundle, with this material I can be guaranteed that the flame will go out once I cut the current.  Those other materials make no such guarantee.

I don't know if the smoke from it would be worse than nylon, etc.(though I don't think so), but if it's exposed to continuous flame in the center fuselage under my seats...  I've got bigger problems than smoke...

Do I overthink things? ;-)

EDIT: When it arrives I will take a chunk of it and subject it to continuous flame and if it smokes heavily, I'll send it back and go for the nylon version.

EDIT2: I contacted the manufacturer about the smoke potential of their flame retardant material and got this back:

"We know that the smoke from this product when it burns is substantially less than the smoke that emanates from the non-flame-retardant products."

Works for me!  Plus I'll still do the test when I get it.  Stay tuned!