This is such a great idea!
Check this out:
1. Click Exhibit options, get your Image Max Size to fullpx, set Uniform width to its highest setting
2. Go to Admin/Assets/Theme/style.css and add
#img-container .over .asset img.lazyload { width: 66%; height: auto; }
* Note that the images may pixelate on big screen resolutions.
Alternatively you can do this:
#img-container .over .asset img.lazyload {
height: auto;
max-width: 700px;
width: 66%;
}
which basically adds a maximum width to your images.
They will scale proportionally up to the point that images reach the max-width.