I run a catless downpipe on a stock catback on my redline, and I love it. Some of the times I wish it were louder or quieter, but the majority of the time I think it's just right. My last car started getting pretty loud towards the end (I think I blew out some of the rock wool or something in the muffler), and I don't want to go there again.
I've had multiple people tell me things along the line of "damn! That thing's a 4 banger?! Sounds great!" Plus, I really like the stock tips on the redline. Even if I went with an aftermarket muffler, I'd stick with the stock tips.