I vote no bumpers. I think the amount of crashing people get away with has gone up exponentially since the rear bumper came around. Sure it’s saved a radiator or two, but caused a significant amount more people not to finish races at all.
The nut is the same whether you use an 11 or a 12.
When you run the 11 you remove the o-ring and switch to a smaller outer washer. You can put a dab of grease on the bushing but they will always be a little noisier than the 12.
Also, avoid cheap aftermarkets, never had a failure with OEM sprockets.
I drove the Rubig up at IMI, and within about 5 laps was over 2 seconds per lap quicker than my stock honda. If your looking to have the fastest kart bar none, get the Rubig.
