I'm used to working with older versions of Photoshop CS, where I 'just save' exr with no options. This previously resulted in file sizes half that of .hdr. In this latest version if I choose to save uncompressed (which I assumed the old versions of Photoshop did?) the file size is a good 10x larger than they used to be. If I save as zlib or wavelet, they're similar size (a fair bit less than a .hdr).
What did the old Photoshop use for compression? Or how can I find out? I don't remember my old exrs taking so long to compress and save either (with zlib) but I might be wrong.
I'm not saving any transparency either (that I know of!).