Different turbos produce different amounts of heat, a T34 flat out will be much hotter than a T4 running low boost so the amount of bhp the intercooler could support would be quite different, the way the engine is mapped would cause the same i.e. amount of boost etc....the core is key too plus restrictions in air flow to the cooler and through the pipework.

People will have run over 600 bhp through them but the intake temps might be high and therefore more boost may be needed for the power which adds more heat etc.

I believe a lot of people think the smaller spec R or other garret cored coolers are the best.