IXIL was going to be my first choice for the Z650, but due to late production release to the US, I went with the Yoshimura. As with any exhaust change, or increase in airflow, you need to have the bike tuned to prevent over lean conditions. Look into a fuel controller such as Rapid Bike, Bazaaz or even Power Commander. It will be much cheaper to keep what you have and get it tuned, than to swap exhausts, and still need a tune. IXIL makes pretty decent systems that are highly popular in the UK and Spain. But, they are straight up designed for unrestricted flow.