8 speed may be just fine, but running it back in the 90's, as soon as 9 speed came out, the supply of XT cassettes dried up, almost forcing you to go 9 speed, today isn't as bad when speeds are changed, being able to source parts from anywhere on-line, add to that Shimano has changed the hierarchy format for parts like Cassettes and BB's so they cross over levels and are much more available.

Looking at 8 speed cassettes available today, you are limited not by ratios, but weight/component level, SRAM's highest offering is the PG850, Shimano HG51/Alivio