I went the opposite way from you...Lower gearing with a 58 tooth rear sprocket, DID )-ring chain, stock counter-shaft sprocket. (My bike is the one in "Hacks" under "Yamahamer thread" Nice guy took several pix of my re-built machine.)
The stock chain DOES suck, but if you are willing to keep adjusting as it stretches, use it for awhile and THEN get a better one.
My thought was that if the soft counter-shaft sprocket wasn't worn yet, a new chain & sprocket in the back might help it last longer.
that the stock chain size is an oddball one, and when my current sprockets and chain are worn I will try to get larger "common size" chain and custom sprockets.
Of course, if the small DID chain holds-up dragging the hack aroudn there won't be much point in going to a larger pitch chan/sprockets.(Remember to check that you don't have sloppy under-size hub/sprocket bolts like I did.)