When a beltdrive fails, you have to replace a belt. Generally when a chaincase fails you have massive issues with drive shafts, jackshafts, the case being ruined, bearings, etc, etc. When the chaincase fails it pretty much locks everything up.
Sure the chaincase is proven but with the belt drive how many had failures on the updated belt from Polaris? This new system has a different ratio and has more teeth grabbing on the top which is where most belt failures happened when you inspected the belts.
I'm going with the 2.6" and belt drive. I don't have any intentions of going with a turbo (mostly because of budget). If you are going to go with a turbo, I may consider the 3" option and the chaincase. I think the extra torque the turbo creates will be hard on the belt drive. In stock or near stock form I think the belt drive will be fine.