I have to say that modern VVT timing engines also depend on all of the factors that you mention regarding oil. Once an engine gets to temp it is going to be very consistent just at the new cars are unless the oil degrades or the passages get clogged. The spring thig is real but it won't change daily. You will get what you get and I don't see rocker ratio being an issue in any way. New cams come with enough lift that even down .025 they will exceed stock 2 barrel cams.