I didn't try the aftermarket exhaust with the factory tune, but I think it is not going to be great. I would not run an aftermarket exhaust without any tuning. Removing the cats and the exhaust valve is a large change in exhaust flow which means a change in fuelling requirements. Likely 10hp more. This may be driveability problems down low, but you do not want to be too far off on AFR under WOT. This is not a lawnmower engine that will run without damage no matter what AFR. To get 226hp out of 1100cc's and 14,500rpm, you would be crazy to think this is not an engine that is highly stressed and highly dependent on tuning for longevity. There are not the wide margins you may think. I would NOT run that slip on with at least logging the WOT AFR to know you are OK. If you are not prepared to put the T800 on as a temporary measure, I would not install the exhaust until you get a dyno tune. With the high compression ratio, cylinder pressures that come from this high of HP, and considering how hot these bikes run, when running pump gas the bike must be a lot closer to detonation than many other engines out there. That's just what I am deducing, hopefully soon I have some actual experience in logging AFR and tuning this bike.
My direct experience with the Jester exhaust and T800 is that at 70mph, I can add 10% more throttle at cruise and still continue to not hold speed. For that to happen, the AFR has to be off a significant amount.