Derating clarification

I want to install 2 Diva 3 way dimmers in a 2 gang box. Both loads will be 100% incandescent. One load is 540 watts and the other load is 230 watts.

If i understand the derating correctly, I can leave the side tabs on both sides of the dimmer controlling the 540 watt load and it will not have to be derated from the 600 watt maximum.

To fit the 2nd dimmer in the 2 gang box, I will have to remove the tabs from both sides. This dimmer will have to be derated to 400 watts. But since the load is 230 watts, I should be good to go.

Is the above correct?

No.

To have 2 dimmers next to each other, both dimmers need to have the tabs removed. You will need a 1000-watt rated dimmer. Think about LEDs, 540 watts is a lot. So much better for the environment/electric bill and you don't have to change light bulbs all the time.