Less than a month ago I set up XT 8-speed shifters with a 7-speed hub and 7-speed cassette. Worked perfectly. Didn't even touch the barrel adjuster.

I think too many people post to Internet forums who don't actually work on bikes, with advice on how to work on bikes! Take out your Vernier calipers and set them at 0.20mm, it's an absurdly small variance. Then using that same Vernier caliper measure the float range of a floating top pulley. Enough said. When you're wiggle is on the magnitude of 2.00mm plus you don't fret 0.20mm