Yeah there was this guy that came to our PCA autocorsses with a Supra twin turbo that made 1000 rwhp. He tried and tried to get a faster time than my 88 944 TurboS. He had two very big problems. It just couldn't put the hp down to the ground, AND don't know what it weighed, but is was heavy.
I thought weight made a lot of difference autocrossing until the day I gave a 300+ pound guy a ride around the course at speed after the autocross. They had accidentally left the timer on. With the 300+lb passenger I matched my FTD. I noticed that by myself my top speed on the long straight was 105mph right when I had to brake. With passenger it was only 95 but could go a little deeper. Was driving the car at the limit cornering in 4 wheel drifts. The car was accelerating and braking slower but making up for it by carrying more speed through the corners. Ended up a tie.
That's when I quit taking all the stuff out of my car like the spare tire to lighten it up and only removed the loose stuff that might get slung around in the car.
Did the opposite with my BoxsterS. Had set a really fast time and between runs took 120lbs out of it, the passenger seat, engine cover/rear speakes, spare. Everything I could unbolt easily. It wasn't .01 of a second faster. I did at one point switch to some heavier wheels that were wider and looked way cooler. It was .5 seconds slower. I looked so much better I just couldn't bring myself to put the lighter wheels on it.
It might make a difference on the track where the speeds and corner speeds are much higher and there are usually less corners. But autocrossing 200 to 300 lbs either way just didn't make that much difference when truely driving the car at the limits.
Note: The Sheriff's Deputy in the top picture was one of the Judges at the local PCA car show. The gut sticking into the frame on the right is another deputy judge but he wasn't in uniform. Also I always thought the boxster needed a big ol wing on the back like Porsche added to the 928.