If you can get more exhaust out (removing the cat), you will suck more fresh air in, that's why you need to adjust the fuel map to not run lean.

The O2 sensor only influences the fuel mix at idle or cruising, under load it switches to TPS fuel maps only and ignores the O2 sensor. The stock O2 sensor is trying to run the bike as lean as possible (14.7 AFR) to reduce emissions and increase fuel mileage. However, it's a narrowband O2 sensor and is limited in how much it can sense and it's output is either add or remove fuel, it can't tell the system how much to add or remove.

So by removing the cat you lean out the mix since you're now pulling in more air, but haven't added more fuel. This may or may not do damage, seems to vary bike to bike. Since the engine is running lean, it will make it also run hotter, not the most desirable situation. This is why remapping is recommended either by flash or PCV.

As for not exceeding 10,000 RPM, whatever, it's your bike. I don't exceed 14,000 RPM on mine since that's what I set the rev limiter to. My shift light is set to 12,400 RPM which is around peak HP. Most times I'm cruising around 5,000 to 7,000 RPM on the freeways and shifting around 4,000 RPM. Not like I'm racing a MotoGP going to work or the store.

As for fuel mileage, 7.5l is good, I get that when I'm going longer distances. Right now it's about 8.0l, but my ride to and from work is shorter now.