For the 2007 rabbit
*header, not headers. Single cylinder bank, only V's and H's have a pair of headers.
Our header flows just fine and you won't find any to be gained from going aftermarket. The exhaust restriction is the catalytic converter and the muffling system.
I'd rather install the Mk6 2.5 exhaust manifold from a parted car. OEM and tubular construction instead of the Mk5 2.5's stamped construction. But ours flows.