A few comments here- I have the DPP headers which are virtually the same as the SSAC's and the rest of the SLP knockoffs.

First- if you're worried about a true show quality finish- I'd consider having the headers coated. There are many nice coatings which look chrome-ish, and they tend to hold their look better as long as you keep them clean (ie not dropping oil on them and letting it burn). As the headers sit- they won't look as pretty as the pictures for even a couple days. I got the usual header discoloration after the first couple drives- but after months and months, they don't look that great. My header flanges have developed a good bit of surface rust (not sure if they're mild steel or just a crappy stainless grade)- and the headers themselves are very discolored. I realize you can buff them back again- but that is much harder said than done when they're in the car- getting in between all the piping and such.

Secondly- I wouldn't say you must lose AC- a lot of people have installed headers without losing AC. I'm sure it varies a lot depending which headers you get- since they seem to be truly all over the place. However, the fact that this is a pretty labor-intensive install is pretty spot on. You're working in tight areas- and dealing with the ebay headers- you don't really know what you're gonna get- especially if you try a lesser known brand. I've seen people have to cut the headers up and have parts rewelded, etc to fit.

Third- I'd definitely avoid the Pacesetter design (those like the first link)- they are easiest to spot by having each set of cylinder banks come down into its own tube with a short Y pipe to combine them. Even the much more expensive 'real' Pacesetters had a problem leaking here due to sloppy manufacturing tolerances in this area leaving too much gap. Granted the latest ones are supposedly fixed- but I wouldn't trust the ebay knockoffs to seal if even the original designers didn't get it right.

Fourth- you're talking you want 300-400 (I'm assuming wheel horsepower since we really can't measure crank horsepower easily on these cars?)- if that's the case, I'd definitely seriously consider a turbo. I know they aren't quite as pretty under the hood due to all the plumbing- but some chrome plated or polished aluminum intake plumbing and ceramic coated exhaust plumbing makes them look decent- and you'll be able to hit your power goals much much easier. Even if you're talking crank hp- 400 at the crank is a good bit with an M90- and you're going to need a good deal of mods to hit that.

Lastly- about the cat- if those Speed Daddy's come like my DPP's, they would bolt in without a cat as-is (they had a 'test pipe' that bridged the gap from the downpipe outlet to the catback. You'd have to install them, and drive to an exhaust shop to get a cat welded in (just bolt the headers on up to the big circular Vband connection) and drive open downpipe to the exhaust shop.

That brings me to one other point- one thing I do like about that design is that you can just undo a single, easy V band clamp at the downpipe bottom, and you can drop the entire catback in one shot (including the cat if you have one installed)- great for the track.

 

From what I have heard...Speed Daddy headers are not a bad header for the price even with the above mentioned problems. And yes stay away from pacesetter or their knockoffs.

As for mufflers...dynomax. That is just my personal opinion.