If so, I'd strongly consider the 50/1.2L or the Sigma 50/1.4 Art. The Sigmas are, generally speaking, too clinical for me, but lots of people like them - it really depends on how clean you wanna go. The 50/1.2L has been around for a long time now. I got mine pretty close to when they released it - it might be old enough to vote, at this point. That's to say that it's been out long enough that you could probably find a copy with clean glass and some external dings for not too much money. Bokeh is completely a matter of taste thing, but I hated the bokeh on the EF 50/1.4. I remember it was ugly/busy enough that even non-photographers noticed it on some photos. Maybe I just had a bad copy? I liked the EF 50/1.8 more, even.
There's also Otus, of course, but used prices on them have stayed surprisingly high. I think there was also a Zeiss ZE 50/1.4 which is probably more affordable. I never tried it. It's probably very good.
If considering the Sigma f/1.8 zooms, you might want to double-check how the coverage is with the 0.64x SB. I remember the 18-35 had a pretty small image circle - the 50-100 is probably a bit better, being more telephoto.