My 09 with just a d&d y-pipe, can, stock intake, and V-force reeds would get a hot spot in the midrange when crusing down the trail between 6200 and 6700 RPM. Vary the throttle a little and you would never see it.
The other place I had to add a little fuel was on the very top end. It was fine for 95% of the riding except for very long uphill pulls, like 15 or 20+ seconds at sustained WOT. Would be fine up to a point and then all of a sudden it would start creeping up.
Could you get by without a controller, probably. But you will need to be cautious of your riding and know that you are not 100% protected from a burndown.