walp-
i do have a decent amount of experience with moto bike chains. smaller bikes less than 40 horses typically use a 520 chain. slightly bigger bikes us a 525 chain and big bikes typically use a 530 chain. there are also different types of chain. el-cheapo non ringed chains, quality o-ringed chains, and super nice x-ringed chains.
without an oil bath, but with semi regular lubing, a quality o-ring or x-ring chain will go for 10,000 miles. x-ring will go even longer.
my kawi ninja 636 puts out something like 80-90 horse, and has had a 525 x-ring chain on it for over 10,000 miles, with decently frequent lubing. though it is about due for new chain/sprockets. and the rear sprocket is aluminum!
i also have a honda xr-600 dirtbike which puts out way more torque than HP, and it has also been running a 525 x-ring for over 5,000 miles. that bike will do throttle on wheelies in 1st, 2nd, or 3rd gear... and it has a ton of chain slack in these conditions due to the 12 inches of suspension travel in the rear end. the chain gets tighter as the suspension bottoms out. now that's some chain abuse! (can you tell what i do in my free time)?
i doubt a ten HP mill would put much strain on these type of chains. they are designed to take serious abuse, massive torque, rain, dirt, road grime, and a lazy rider that never lubes em, or cleans 'em, yet they still seem to work flawlessly for long durations.
in my mind, a moto chain would be the ideal candidate for a geared unit. i'd be willing to bet you'd get decent lifespan out of an x-ring chain with no oil bath and periodic lubing, though i wouldn't recommend it. oil bath is far superior!
when i read of moto chains, i just had to add what i have witnessed. i'm continually amazed at what moto bike chains can withstand, yet they keep on ticking!
on a seperate note, shaft drive rear ends on moto bikes require less maintinence, yet they also deliver less power. IE: when's the last time you saw a shaft drive moto GP bike??? or any race bike for dirt?
adam