The side plate thickness does vary as you go from regular duty to heavt duty chain, but a duc is heavy duty specced anyway. The only difference between an o-ring and an x-ring is shape The x-ring is better because it gives a pair of sealing surfaces, and hence is better at keeping the original chain grease inside, and is slightly better at keeping cack out ... as long as you keep your chain clean(ish) ! All this adds up to less adjustment required
Did a quick search, and read one of Shazaam's old posts about going from 525 to 520 on a 999, and he didn't recommend it due to the torque and weight of the bike. I know mine is a 749, but it weighs about the same?
Im not bothered about being too trick, 525 will probably do me fine, the extra 2 teeth should provide the change I want
Yeah, Alan at AJ Racing has confirmed what Shazaam said about needing a longer chain, an extra 2 links and a slight increase in the wheelbase should sort it!