According to the charts, the TBM's WEP it has a small effect on both speed and climb, up until about 5K, after which it dwindles to nothing.
For example, I've just maxed the TBM out at 260mph at 3K. If I engage WEP the fuel consumption goes up, and the TBM accelerates to 267mph, which is pretty awesome. If I disengage WEP the TBM slows down again.
I assume that, historically, the power boost was dead handy for taking off and landing on a carrier.
