Single muffler or dual exhaust better for v6 mustang?
Dual 2.25" pipes were OEM on the GT Mustang, so a single 3 inch would be fine on your V-6. However, the problem with 3 inch exhaust is getting it bend over the axle without crushing it. Dual 2.5" pipes would definitely take away bottom end from your ride.
Short answer, one large pipe will flow as much as two smaller pipes.