i believe 2602 from mega or max(same pipe) works the best.
The 2620 makes the engine perform a bit flat, it performes ok in all ranges but no real grunt.
The 2602 wil give the engine more mid and topspeed.
then you have the 2601 which works good aswell, but it's totally focused on top speed.
I always use a short conical header(5 fins).
And don't try the 2630, its completly shit. If you want any decent performance out of it your engine will overheat.