The regular GNs were pretty fast as well. G-body cars in general can run a strait line with the best of them. I have an 86 SS Monte Carlo with a mild street engine, 350hp 355cid. I would venture to say it would run right with a stock TT. Hell I raced pretty much everything else when it was my DD. The stock curb weight is pretty much the same as a TT. The buicks actually had a lighter cross member in them. A bunch of circle track guys I knew would swap them. They put power down pretty well and have good weight transfer off the line. The best thing about a G-body is you can stick a big block in it without any modifications or fabrication. They sure won't handle the corners like a Z will. And the weight distribution sucks.