Ektachrome 400x push performance?

I exposed some Ektachrome 400x at EI 1600 in a dark indoor horse arena (deep shadows).

Should I request a push process of 2 stops, 2.5 stops, or 3 stops?

Thanks.

The E6 lab I used for decades before they closed shop always told me that pushing transparency one-stop isn't one-stop. It's only 2/3 of a stop when it comes to development time.

Believe me, I never did the high math, they tested it all with control strips and did the charts, so they knew. So 400 to 1600 to you and me appears as 2 stops, but it is really 2 2/3 stops according to their densitometer readings. So I'd process the film with a 3 stop push to be on the safe side. If you have more than one roll of film, perhaps to a clip test.

this is similar with pulling E-6

I have shot Ektachrome 400X like that once in the past. It did not seem to perform quite that well under push conditions, so I have since moved on to other films. In general, one stop push would be for ISO 800, and two stops push would be for ISO 1600. However, I would suggest an extra 1/3 stop push for shooting under night conditions, since I think only getting a two stops push might result in somewhat dark images. If your lab does 1/3 stops, or if they do decimal stops (0.3), then you have that option. Definitely ask your lab for advice on this.

Ciao!

Gordon Moat Photography

Thanks everyone. 3 stop push is what I will ask for.