My Vers suffered from lean surge at 4000 constant throttle cruise. O2 eliminator sorted this out by not leaning the mix at constant throttle mid revs. I've read that the O2 sensor tries to lean the mix to 14,7-1 at cruise speed to get best economy, but this caused driveability to suffer on my bike. Even at 2800 I had a slight hesitation when applying small throttle from closed position. Its all sorted now.
No need to decat or swap cans, unless you want more noise like I did. It makes no difference to the power availability or delivery. Strange but true.