I put a 991 on my 9.9 straight off. Thus far (600+ miles) the chain has been fool-proof. I won't say I "love it" or that it's the best chain I've ever run cuz I ain't like that... I will say that if/when I need another, I'll purchase it again.
I pack the OEM chain (Shimano dura-ace) as a spare.
I pack the OEM chain (Shimano dura-ace) as a spare.