One other thing...what's the diameter on the stock pipe? I presume that my exhaust system is stock, but the pipe's already pretty bloody big. I think it's either 2 3/4" or 3" as it sits...certainly bigger than the 2 1/2" pipe on my truck (with an engine that's double the size of a 617).
I do believe that the more restriction-free you can get an exhaust system, the better (if nothing else, to allow the engine to work less to get the exhaust out, thereby lowering EGT's), but short of straight-piping
I'm not sure what kinda gain you would get out of modifying the exhaust...seems to me that Daimler-Benz already did a lot of that.
OTOH, I think that steps could be taken to make the intake more restriction-free...