Here's what I've gleaned from searching around for you-

You're right, difference between the 5mm and 8mm versions is for different dropout thicknesses (usually for steel v. aluminum frames).
A bunch of crap in jargon I can't be bothered to decipher.

E: If you're not set on the MKS ones, Either These or the diamond back ones in the related items would certainly have enough travel for your application.

FWIW, I don't use a chain tensioner, rather I use track axle nuts (the ones with a captive washer). Even when I raced BMX, they were more than enough, and I found them easier and quicker than messing with a tensioner.