2008 join date and this is your first post! Dang.
I'm actually in a similar situation myself. I could basically replace 2 or 3 of my lenses if I bought a 16-35 II. That would be my 24 f1/4, 17-40, and to some extent my 15mm fisheye. The ISO on my 6D is good enough to where I can just crank it up a bit more when I need it, plus I will have the versatility of a zoom. I mostly shoot concerts and I'm usually shooting at f/2 (on the 24, my 50, and my 100) to get the most out of everything but one more stop wouldn't hurt too bad.