Auctiva does store up to a 1024 x 768 original image, so that should operate correctly with the new standard header image.
The last time I looked at their image box, it was 500 x 500. The discussion of "zoom" function with 1000px on the announcement has me curious too.
This is the 3rd (and hopefully) final incarnation of "New Design", so anything is possible. Versions 1 and 2 were well, let's say, less than enthusiastically received by the masses.

Danno