If you planning to remove the cat converters, then make sure the sensors are properly placed accurately to avoid lean mixture of fuel or else say goodbye to FC.
3-1 is our stock, go for stainless. 2" outlet is the maximum you can get for muffs of else you will lose torque.
If you're after for throttle response, there's a lot of ways to increase it without compromising your exhaust system and ride/noise comfort.
Our celerios are capable of running 190kph and even more on stock engine. See on youtube or team celerio website for proofs.