To be honest, there's very little in it. I've spent months looking at reviews of it, DXO scores, their reviews, user reviews, real photos, positives and negatives and after all that, I decided to not bother getting the 50mm when it comes out as I haven't once needed that focal length on full frame. I miss the look from the Sigma lens I had on the 60D (50mm 1.4) and decided that I can get this and easily sell the 35L if the Sigma is as good/better than it. My main reason though, is that the 35L doesn't feel as nice to use as the 85L and while the images, as you'd expect are great, it's just not quite sitting right with me. Probably my frame of mind (no pun intended!) really but as I'm in a position where I can buy it and at the very least if it's equal to the 35L, sell that and get my money back, I'll be fine and wiser for the experience.
Either way, one is being sold, unless I decide to give my dad a prezzie.