400 Nitro is correct.
I have a 450 No2 extractor double, a 450/400 3 1/4" ejector double, and a 9,3x74R ejector double.

I have switched between the extractor 450 and the ejector 9,3 on the same day, on 2 Safaris without problem.
If you have strong feelings about ejector vs extractor get the one you want.
I know it would not make any difference to me.

In a timed test you can load an ejector gun a little faster, but I usually catch my brass from my ejector guns and put it in my back pocket any way.

The thick vs thin rim thickness is not an issue with modern cases to me either. Both work.