My original headers and side pipes had high spots of weld near the center.. The original assembly ended up having the gaskets blow out quite easily as the torque of the bolts around the outside corners simply pulled the metal to bend and leak around assorted areas. The gaskets burned out pretty quick to get noisy. The center burned out pretty good too. At the time I pulled the parts and ground them flat with a belt sander so they were flat to a metal straight edge. That worked pretty good with new gaskets and changing to good solid high grade bolts with lock nuts. Just plan on a new set of bolts and gaskets each time you pull the side pipes. It's a better job that way.
When I switched to new headers which didn't cover 1/3 of an inch width of each exhaust port like the original Superformance headers the new had a low spot of maybe 1/8 inch in the center were they attach to the side pipes. I cut the center of the gasket out knowing that all four pipes would have a cross over point at that location. I'm not sure of the science or theory that might be behind having the pipes with a slight internal leak between all four pipes, but it seems to work. All of the lengths of pipe before the collector are different anyway. For whatever reason it seems to work well.
When I got the Buckshot Racefab side pipes the surface which mates to the headers was perfect with clean welds and a perfect flat surface. I've not had an outside gasket leak yet, but still do have a low spot in the center of the header side of the connection. Here is a link from my gallery of a dyno pull. The pull has zero smoothing for display and would be corrected values.
http://www.clubcobra.com/photopost/d...3_wheel_HP.JPG
Torque and Power is pretty good, maybe better with the little space, who knows? I'm not going to worry about the center. Exhaust is weird at times.
I've ordered new gaskets from the Olthoffs and the place out of California for a good value. I keep a little stack of them around the garage.