There is a difference between the F2 and the OBX/Focussport headers. One being the primary size. The F2 uses 1 3/4" primaries whereas the others use 1 7/8" primaries. This creates different breathing effects on the motor. The F2 will retain more of the cars around town driveability as the peak torque will arrive earlier. The OBX/Focussport is more helpful with the high end HP generation but will also help flatten the torque curve. So you may have less peak TQ with the same car/same mods with the OBX/Focussport but the torque generation will be much more linear.the obx is also pretty much the same as a cossie. thats what i have. right now your options for a brand new header are obx, which is the cheapest. next is the f2, then the focussport. all are good. if you wanna save money, get the f2, the obx isnt bad but for the price difference i would go with f2. f2 was about 400 when i got my obx, which is why i got my obx.