Yep, thats what I have seem in your country and Europe. I pull a 14.5 foot boat with a 40 hp side console at less then half the max rating with no brakes and that is all I would every want to pull. I assume you have brakes on your trailer?
Really depends on trans and brakes... IMHO I would never go past 900kg on any stock Kona even for short distances... The auto trans and electric will probably have the best luck with towing anything. After that it's the brakes, so far even with my brand new factory brakes are lack luster to say the least. I plan on moving to the CTSV/Gen kit after that I could see that 1200kg being "OK" to tow for going across town. For anything worth stating on distance a trans-cooler would be needed. But that is in the states and I'm in Kansas, we have higher average speed limits.