Re: thinking bout an 8 spd sturmy
The SRF-3 and SRK-3 have 3rd gear as direct drive, and then 2nd and 1st are underdrive. When the indicator chain is relaxed, the clutch engages the planetary pins and the carrier drives the shell. I've had success with 1000watts electric in a 16" diameter wheel, but shock loading it offroad cracked the driver, which spread the freewheel cover, which jammed the clutch, which stuck it in between gears, which broke pawls. It seems everything is hunky dorey until it machine guns all the guts because of a sequence or combination of errors. The thing I don't like most is having to be gentle on throttle and not crack it wide open from a stop, which is horrible for it if you're in 1st. If you ride carefully it could last you years though, the gears looked okay.
I say go for anything without pawls. The Sturmey/Shimano cogs with three drive nubs like to fatigue shear and fail, so using a hub with a strong cog mounting is important. I went through 3 Sturmy 16t's with an 80t #25 bolted to it, hopefully that will be a thing of the past since I fixed the chainline which was off due to the hub not being adjustable in chain line if you've got a really wide swingarm. The Shimano sprockets look like they're less beefy than the Sturmey ones, but they might have better mettalurgy.
KTM50 Schwinn Chopper - 6000W E-Motard - 52cc Auger BMX - 9sp+CVT 52cc Cagllari Moped