PP advice is correct.
I hit in the 70-80% range for vast majority of shots. Will go up to 80%-90% in certain situations. For example, 1st serve at 40-0, aggressive 2nd serve with score in my favor, or FH sitter; may all go up to 80-90%
Key for me is to never decelerate. If hitting at 70, 80 or 90%; I must start at 10-20% and accelerate into the desired level. Start smooth and accelerate into contact is key to maintain control and spin.
Trying to play at 90-100% of maximum RHS all the time would result in too many UErrors for me, and I would be tired by the end of the 1st set.