Muffler restriction is generally more than the pipes. What muffler are you running?
If you drive the car mostly on the street, and the muffler(s) are near the rear axle (away from the headers) 3 inch back to efficient mufflers (most 3" Magnaflows) and then 2-1/2 behind the mufflers will be powerful and relatively quiet.
If you are running a less efficient muffler (most F!**
[email protected]$%%%s), the 2-1/2 pipes don't really hurt.
As the exhaust cools travelling from the engine to the tailpipe outlet, perhaps 800+ F°, the volume decreases. You lose a bunch of that heat across the muffler, so the smaller outlet/tailpipes don't hurt much.
The farther from the engine you put the muffler, the less power it robs for the same^^ reason.
Jon