I’ve played around with valve lash on my E4 all the way up to 0.025”. Although the idle characteristics and general drivability is very good at 0.025”, the valve train is excessively noisy. I currently run the lash at 0.019” and there is still some noticable noise from the valve train but not near like it was at 0.025” lash. At 0.015” lash, the rumpity rump of the cam is much more noticable but I did notice an increase in fuel mileage running the lash slightly looser than what was called for. Like Dennis says, the cam does call for 0.015” and best wear will likely occur with it set there. If there’s noise, there’s some hammering taking place so keep the noise to the minimum.
“Do as I say, not as I do.” My Father, ~1963.