Well, I can help ya out there... basically, the "sport" system is a low cost fully-stainless steel system. They don't make it for most of the hardcore sportbikes, and it's not available for the 636.
Which leaves you with the slip on system, the Racing system, and the Evolution system. Akrapovic only makes titanium and carbon fibre cannisters for the 636 systems. First step... decide whether you want carbon or ti for your endcan material.
Next, if you want the FULL exhaust, you have a choice between two high-end racing exhausts... one uses titanium throughout... from the heads back to the endcan, and that's the EVOLUTION system. The RACING system is the exact same in terms of engineering power, except it uses stainless steel exhaust pipe from the heads back to the cannister. Both put out identical power, but the Evolution system is lighter (full ti), and more expensive.
Be warned, you WILL have to remap the fuel system to take full advantage of the new full exhaust. I have seen some Akrapovic race teams are using the new Techlusion system (
www.techlusion.com), but the Power Commander units are the most popular by far.
If you want a slip on system instead, you can get ti or carbon cans, and your choice of ti or stainless link pipe (all the pipe you can see outside the bodywork). Slip ons will not have as dramatic an effect on peak horsepower, since it takes re-engineering the exhaust system in full to change power characteristics, but the increased airflow means you will get a gain in rev capability, and a slight boost in power in the upper portion of powerband. The tradeoff of the increased power of the full system is a slight sacrifice in low-end power (sub-5000 rpm). More than offset of course by the LARGE boost in peak.
"Keep yer feet on the pegs and your right hand cranked."
