Sorry for the long spiel, but I can't shorten it any other way. I apologize now if I'm preaching to the choir...

It's not so much you "lose" on the lift shift, it's what you don't gain. The "proper" way to shift a car with minimum drivetrain damage and stress is to take to take it to the sweet spot in the RPM range, lift of the gas at the same time depressing the clutch (so smoothly, it's as if it never happened), and shifting than re-engaging the clutch at the correct rpm point w/o losing vehicle momentum or disrupting the engine revs (or even having the car shudder. Think of it as a proper engagement of the engine, transmission, and rear wheels). Can actually be very tricky under engine load.

Powershifting/speedshifting or quick-lift shifting do the opposite- they cause the car to jump, shudder, and more often than not-leap forward a few feet.

Example ever do a "neutral drop" on a crappy car with an automatic...? You rev it up in neutral, and than drop it into drive from a stop? Power/speed shifting is the same thing through all forward gears having a positive effect on your timeslip-your engine brifly overrevs while the clutch is depressed, and as you re-engage the engine rotational momentum cause you to leap forward. Bad news...? Your engine, clutch, trans, rear hate life-especially if you miss the next gear-it equals overrevved engine, worns synchros, metal shavings in your trans fluid and a look on the spectators faces that says it all. OUCH!!

So by quick lift shifting, I am banging my shifts fast w/o danger of an over-rev or smoked clutch (C5 weak points, along with the shifter) but I since I don't quite match the revs in time (they are still up at 5800 rpms) the engines rotational momentum cause the tires to bark as they try to match 5800 in the next higher gear in .25 of a second. With my foot off the gas, the revs get yanked down but I'm still into the car's momentum. So I don't lose-but I don't gain either. At the track with the runcraps I had to slow that shift down even further-if I disrupted the suspension by breaking the tires-I would get violent wheel hop.