Duals would give you an improved flow would they not?

 

Well it wont be a "true" dual exhaust, if you look at that muffler I gave the link to it is a single inlet and a dual outlet.
So at the back it will look like a dual exhaust with both tailpipes being side-by-side terminating in the same spot as the OEM exhaust.

 

A couple of things to think about

If you use flex pipe, you will have to support it more. This system does not have a ton of hangers, and if you add some flex, you will have to add hangers to support.

The majority of your quietness is in the rear "resonator" If you want flow while remaining quiet, get a Flowmaster Delta muffler and have the shop replace your resonator with a new one. You will get a quiet deep sound. My VW just lost the rear resonator and I had a new one welded on with the pipe repaired for $60.

The key to anything is finding a good small muffler shop. Midas will charge out the wazoo for exhaust. I was quoted $250 for the VW there and I am friends with the owner. Prices are set and they will not work with you. I went down to "randy's muffler" and caught him in a slow spot. $60 and he did it right away. Find a small shop and drive by until there isn't anything in the bay...

 

X2 on finding a good small shop. Mine built the entire exhaust from the headers back (custom y pipe with a pair of magflow cats, to a flowmaster 40 muffler) Including installing the o2 sensor bungs behind the cats etc... total cost 100 bucks

 

dang I wish I had found them when I did mine

 

I have a small shop, I am friends with the owner, a case of beer and I buy the parts and the job is done.
The muffler will be the most expensive part.
http://www.holley.com/21106HKR.asp
Pretty sure thats the one I am going to get.