BE bearings state that the increased clearances in their bearings is designed with 10w-60 in mind. From there website :-
Designed to address and fix the rod bearing clearance issue.
Designed for use with factory 10W60 weight oils.
So 5w/50 shouldn't be needed for the rod bearings, RomanK makes an interesting point about the main bearings, but as Helmsman says they are far less likely to fail.
Also, 50 grade oil will shear (wear) down to a 40 grade oil (typically) after a few thousand miles or so, not sure that 40 grade will be ok in the long run.
Maybe when RomanK has done ~100+k kms on those BE bearings, & if he strips it down then he can show us how they did with 0-40, he's 1 of our guinea pigs
(no offence RomanK
).