I am studying automotives... Gonna go ahead and hope that I have valid knowledge to chime in for this.
First, read this:
http://www.epi-eng.com/piston_engine_technology/bmep_performance_yardstick.htm
BMEP is not correlated to actual chamber psi, and, it is simply a rating. Kind of like the term "horsepower"; it is not directly usable in the real world, but it is a rating.
Anyway, seeing as BMEP is nothing more than a rating and is not actually related to the real cylinder pressures, there is NO point where a higher BMEP would equal less power. It will always mean more.
If, on the other hand, you mixed up BMEP and whatever term you wanted to use for actual cylinder pressure; again, there is no point.
Pressure in an engine is measured by the volume of air in the chamber at BDC, and how much pressure is generated at TDC. This works with two variables=
How much air is in the chamber, and, how much it is compressed.
How much air is in the chamber is controlled by many things. They are largely modified by superchargers and turbochargers just as you said, but, simple airflow changes such as new intake manifolds, cams, exhaust manifolds, carburetors, etc. also affect a term called "volumetric efficiency", or, for your uses, how much air is in the cylinder. So basically, ANY MOD touching ANY of the gasses going in or out of the engine will affect VE (volumetric efficiency.) Yes, this includes the piston itself and the cylinder walls.
How much it is compressed is simply measured in static compression ratio.
Either way, more psi is always more power; while it may also equate to more heat, gas usage and other bad things, more pressure means more force; and more force means more force pushing the piston down and therefore resulting on the other end of the crankshaft, and, eventually, at the ground.