I currently race in KA3 junior light (using Iame KA100 engines with a 22mm restrictor). I am using a 2021 model Kosmic Nordix junior kart. I have almost outgrown my current kart, and will be looking to upgrade to a senior chassis at the end of the year, most likely an OTK again. I have heard some people say that a senior kart in some cases may pick you up 0.5 to 1 second in speed compared to a junior kart. I have actually seen myself one of my friends upgrade to a senior kart and gain a full second in the process.
Senior karts are a lot more stable and have more room for improvement in setup and chassis. Especially for KA3, you will find that you’re able to make more changes to the setup and handling of the kart and it will feel a lot more in control, and stable
It seems most juniors in Australia have now gone to senior chassis due to the extra HP that came with the restrictor change at the begging of the year.
If your buying another chassis id defiantly suggest getting a senior kart of which ever brand you choose.