Hyper Glide as per Sheldon-
"A system of
ramps and special-shaped teeth on
Shimano rear
sprockets that permits much smoother shifting than older systems.".
I don't think Shimano made an 8 speed FW.
I'm running an 8 speed on 126 spacing. I think my OLD is actually about 128 after transplanting an 8 speed FH body to a 7 speed system.
As far as using the RDER, I'm using the stock "Deer Head" on my 86 Rockhopper.
A lot depends on the travel AND WHERE the travel is.
On a different bike,I transplanted a 7 speed FW in place of a 6 speed. I had to add a bit of spacing to the drive side to get the RDER to reach the smallest cog. I had "oodles" of extra travel past the largest cog. It WAS tempting to just bend the drop out/hangar.