No reason a "smaller" chain won't handle the power, 520 was plenty good enough for all my harleys, best answer here is to educate yourself somewhat and then make your OWN informed decision, it is after all YOUR ass that will go sliding down the road if the chain snaps, jumps the sprockets or piled up in front of the front sprocket and shags the motor casings...
strongly suggest you read and bookmark ALL these links
http://www.motorcycle.com/mo/mcnuts/chain.html
http://www.ustsubaki.com/chainguide.html
http://oldmanhonda.com/MC/Rchain.html
http://www.dansmc.com/rearchain.htm
HTH etc
cheers
(PS, FWIW I'd run a 520 on my TR1, only reason I didnt was the extra hassle / expense of changing the front sprocket too.. which wasn't worn out.