My engine was rebuilt and has all new seals so no problem with leakage.
On start up after changing the oil the engine sounded quieter than before, I can't explain why but it was....... That said it still sounds like a bag of spanners being rattled but it's a smaller bag.
I did this after speaking to the oil technician and up to now no problems, no increase in oil usage, in fact I don't loose any oil at all.
Personally, I wouldn't go back to a single weight and prefer the extra benefits of having a better modern day specification oil.
Born to cruise...........once forced to work!