Actually, a sparky and the stock silencer seemed to be what Team Green that was the best exhaust set up. Destry Abbott's 2004 KX 500 had the stock silencer with three inches removed from the end and a sparky welded onto to it, even though he was sponsored by FMF and had their Gnarly Desert Pipe in his bike. I remember hearing that Team Green claimed this was the only setup they tested that didn't result in horsepower loss compared to just using the stock silencer. Just the fact that this setup was on a legendary, winning machine has some merit.
After repacking my FMF Turine Core, it sure did appear as though it was pretty restrictive with the internal bend in the spark arrestor. IF anyone knows where to get a brand new sparky for a 2004 KX 500, please let me know because I have the stock silencer for my bike and would love to modify it and test it out.