I’ve been road racing an 07 leopard for the last couple of seasons and typically run about 16 inches from the header to the first weld on the expansion chamber. I’ve not noticed much additional pull going longer.
I would suggest trying a taller gear to drop some rpm though. Leopards make peak hp between 12.5 and 13k rpm. Spinning them much higher will actually lowers your straightaway speed. On big tracks, I typically gear for about 13k max rpm running alone. This can equate to about 13.5 or so in the draft. You will be amazed at how this can lower your lap times if you keep your cornering speed up.
Check out my videos at l8apex63 on YouTube. Some include engine rpm.