Graduation ceremony will be in a large college basketball stadium, so distance and low light will be needed.
The concert is going to be dark but it'll be in the floor area, so possibly can get some good close shots. Low light will take priority here.
Was thinking 70-200 2.8L II for the graduation and the 135L for the concert.
First...NOTHING slower than f/2.8
A few weeks ago, I shot at Voodoo Fest in New Orleans....3x days of concerts and I had credentials for full access to pits and even backstage. Concerts in day and night.
My 70-200 f/2.8 L II was the workhorse....but in some of the stages it wasn't too high and I was right up close, I had rented the 85mm f/1/2 to play with, and I got decent shots with it...but I found I was switching between my 70-200, and mostly during the day...my 17-40 f/4 I own, but it was a bit slow at night. I ended up getting some interesting shots (again, on stages I was very close on) with my cheap-o Rokinon 14mm f/2.8.
And even on some stages that were higher, I could set that thing up (manual lens) and just hold the camera up high as I could and shoot...and I got some good keepers with that.
If you're renting two of the lenses, I'd say #1 for sure, get the 70-200 f/2.8. You might look into either the 16-35mm L f/2.8 too if you want to have a spread between wide and tele....or in lieu of the wide zoom, maybe also rent the 24-70L f/2.8 II lens.
Those two should cover you pretty nicely....they worked for me and this was my first real concert shoot I'd ever done.