Boost over 15psi is not bad as long as EGT's are low enough, and cylinder pressure is not insanely high. People have beefed up OM617's with 25-35psi of boost and gotten plenty of power. The problem is the cost and the labor time - many thousands of dollars and hundreds of hours. Very low ROI! More boost heats up the intake charge and makes intercooling more of a requirement, not an option, as boost rises.

FWIW, Mosselman's kits leave the stock boost setting and simply enrich the pump internally, and get the aforementioned 20% power gain safely.