Here is the deal on powershifting - do it a whole lot, and you will no longer be shifting into an actual gear, you will go into the gear, give her gas, and you will go nowherez. All it does is kill the gears inside of the transmission. As far as engine damage goes, it can hurt that a lot if you can't shift fast enough, as in bounce off red line and all that stuff... so yeah, if you do it, be REALLY quick about it.
Absolutely kills your clutch when you powershift, no way around it.
Is it really faster? Yes, its quite a bit faster, if you are really good at performing a powershift, it can give you the edge in a race if you are racing a car that is equivalent to what your car is (like if you were racing a car that had all the same mods as you did, or if your in a stock car racing another stock car with almost matching stats).
My friend powershifted his Mustang in every race, and he ended up swapping transmissions every few months. It wasn't much of a drag car or anything like that, just a really loud 302 with a 5 speed - and he drove the piss out of it.
All I can really say is, if you want to powershift - do it right, or don't do it at all... its not worth it to do it until your desperate. I have been desperate before a time or two in my 944, I was doing first to win 3 races with my friend once, and he got me the first race... and I knew that there was room for me to get him (nose to nose racing), so the 2nd race I just raced him like normal (waited on him to screw up), and he didn't, so come the third race I powershifted and got about a car ahead (when the other races it was nose to nose). I easily got him the other 2 times doing the same thing. So it really is affective, just make sure you do it right, and its something you do when your desperate.
