I have a DC Sports 4-2-1 Ceramic on my 94 GS-R... it's OK, and I'm sure they improved performance a fair amount... I put on my exhaust at the same time, so I can't tell exactly what the headers added.

Though, I mainly got it to eliminate the noise that came from the doublewalled stock headers, and I got mine for $220 shipped, which is not a bad price at all