Nope. Several reasons:
1) increased underhood heat, always unwelcome (esp. with a compressor there)
2) the stockers ain't bad at all
3) Downeys would prevent a behind-the-heads crossover, forcing a crossover behind the transfer case (waaaay back in my case, with a crawler, paralleling the fuel line <img src="/forums/images/graemlins/scared.gif" alt="" />) and forcing either dual converters or rearranging the whole exhaust
4) durability. Cast steel is hard to beat. They also have increased heat retention improving scavenging, though I doubt I'd notice. Redoing gaskets is something I'd like to avoid. So is Downey in general.
5) noise
6) more expense, like I needed that.