[Perfectlap]

I'm guessing your about 270-280HP at the wheels.

SPortec put a 997 3.8 in the 987 Boxster (aprrox 350 HP) and Excellence said it could have easily handled much much more.

THe car definitely comes "alive" out of corners when 250HP/Torque or better is under there. I've driven various roadsters between 130 HP and 300+ (I forget what the Dinan MZ3 had) and there's definitely 'sweet spot' in the power to weight ratio.
Most well balanced roadsters handle superbly like a land shark with less HP but a roadster of roughly 3 tons at 240 HP and better has an extra kick in the pants.
My local autocross club put the 986 BoxsterS in with the 3.4 and 3.6 911's.
I've equalled or bettered them on many ocassions. The 2.7 Boxsters on about 20 less power than the 4 cylinder S2000 go back and forth for quicker times. The M3 coupes seem to post similar times to the standard 996 anbd 986S.

I think what you feel is that crossing over that sweet spot (which really doesn't affect peformance as you see with the S2000 match up) but changes the seat of th pants feel entirely.
Kinda like a 3.5 - 4.0 ton coupe when you cross the 500 HP in straight acceleartion. 350 doesn't feel much slower than 450 but over 500 and it's like "wow!"