I got my custom dual side exit exhaust done now too. Very aggressive sound, especially when on the gas. By 1/2 throttle it is a good low rumble. There is more exhaust noise heard in the car with the pipes coming out just behind your hips but this is to be expected.
No problems on spool up either. I could see how a really restrictive system would hamper spool up but the more free flowing the better. Just look at the test pipe dumps, no problems spooling there.
I ran mine as simply as possible, altogether I have less than $200 in it. Could I have gotten the pipes 1 piece and bent, for sure. But this works great. To each his own.
Here is a couple pics from under the car though I changed the hangers around to pull it tighter to the floor pans. If need be I will install a heat shield above the muffler. I kept the test pipe dump option open for later too.
And I have all my original exhaust pipes unaltered so if I ever change my mind I can rehang in an afternoon.