Side Exhuast Muffler Shootout

I'm trying to figure out how to make my side exhaust work. Right now I have BBK long tubes for a fox going into a Dr. Gas o/r x-pipe with a MAC catback. I have Roush side skirts and plan to run side exhaust similar to TurboGTs but I’m trying to keep it as quiet as possible but with a straight through muffler. Most side exhaust setups go into a chambered muffler than back around to the front and out the side. I’d like to avoid this extra confusion and use a straight through then right out the side.

TurboGT’s pics can be found in this thread: http://www.stangnet.com/mustang-forums/763907-longtubes-x-pipe-stingers-pics-vids.html
I’d like to stick to this basic layout as it is pretty much exactly what I had in mind. The tips I’ll be using are Borla angle cut intercooled dual tips that I’ll be cutting and turning 90 degrees.
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I’ve racked my brain going through and trying to find all the info I can on mufflers.
-Magnaflow Round – 4” round, 2.5” in/out, 20,24,28” long. Same mufflers used on their magnapack kits. MagnaFlow Performance Exhaust
-Borla Stingers(S-type) – 5” round, 2.5” in/out, 10” long.
-Borla XR-1 - oval, 2.5” in/out, 12” long. Quieter than stingers but oval. 83db at idle, 96db at 2k rpm, 118db at WOT. Don’t have their 5” round in 2.5” in/out, smallest is 3”
-SLP Loudmouth – 4.5” round, 2.5” in/out, 18” long. Resonator. Loud. 10/10 loudest according to SLP.
-SLP Loudmouth II – 4.5” round, 2.5” in/out, 18” long. 7/10 according to SLP.
-SLP PowerFlo – 5” round, 2.5” in/out, 9” long. 5/10 according to SLP.
-Dynamax Race Bullets – 4” round, 2.5” in/out, 12” long. “4db quieter than most race mufflers” What is the db on race mufflers though??

Correct me on some assumptions if I’m wrong here. The longer the muffler the quieter it would be right? So in theory the Magnaflow that is 28” long should be one of the quietest. Also subsequently a 5” would be quieter than a 4”. I’m thinking this is the way to go here. If I don't even have that kind of room I'll be going to the SLP PowerFlo.

I’m leaning towards the Magnaflow after all this purely for its extensive selection. I should be able to measure “stuff” and see how big of a muffler I can fit in there and then get the biggest from them. The other vendors have very specific sizes that I’d be stuck with. I'm planning on taking extensive measurements this weekend. Can anyone think of a muffler I’m missing other than serious race mufflers? Again, quiet is the key here, not so much tone.

i realize 28" is really long, I was more making the point of bigger is better. and yes I could go with the chambered route but the u-bend to get the tips to work just doesn't seem to be effective to me. the tight radius of the bend is worse than over the axle. Granted I make enough power as it is with the blower and whatnot but I want as free flowing as possible.