I havent posted anything on this site for a longass time, but since I have an 07 S2R 1000 and went through this a few years ago, I thought I would add my 2 cents. I bought mine used and in good condition but it already had the cat removed and aftermarket exhaust installed. The slip ons were Arrow, and they were loud as FUCK! I actually had to buy dB killers from Arrow directly and inserted them into the cans to reduce the noise to a tolerable level. As far as the performance of the bike with this exhaust, it took some time to get it dialed in right. When I first got the bike, it ran like shit; stalled at the shop I bought it at even. At the time there were no canned maps on Dynojet's website and I did not feel like spending $300 getting it dynotuned so I did some research and borrowed an Power Commander autotuner from a local shop here in seattle.
I dont remember which map I ended up using specifically, but I tried a number of different maps from an M900, the dynotuned map for my old M750ie, an 848, and a multistrada. I basically let the autotuner suggest trims until my AF ratios were around 13.5:1 all around. I should mention that the autotuner threaded into a bung on each header like an o2 sensor; I would do several rides with it on one header and then move it to the other header after making adjustments. I'm also using a Power Commander 5 and the autotuner plugged directly into it.
I've been using the same map now for years and the bike runs great. If you want to try my map, you are more than welcome to.
2007 Monster S2R 1000
Past: 2004 R1, 2001 CBR F4i, 2002 M750ie, 1973 Honda CB500f
"I feel sorry for people who don't drink; when they wake up in the morning, that's the best they will feel all day" -Frank Sinatra