What to add to my kit?

So i've got all the gear in my sig right now, but I've been yearning to change or add something. I mostly shoot portraits and events so and 35 and 85 are my bread and butter.

Would it be beneficial to have a 50mm (probably sigma) even though I've got those two lenses?

So i'm a bit torn between upgrading my 85 1.8 to the sigma 85 or adding a sigma 50.

Would the sigma 85 be a substantial upgrade?
Would a 50mm be redundant in my rig?

thoughts and suggestions welcome

What sort of events ? 70-200 2.8 IS II I would recommend to anyone that wants to shoot in that focal range.

in particular, weddings and parties. so i'd like to be fairly up close to the action.

I'd stick with the 85 you have, and like Chewie said look at one of the 70-200's, 70 will get you in close.
I tried 3 Sigma's 50's, beautiful looking & feeling lens but unfortunately none of the copies I had worked. 3 was my limit, both I and Amazon were getting tired of me sending them back.

a 50mm is not redundant unless you already have a 50mm or a zoom that covers that focal length.

are you happy with your 85 1.8? if so then maybe a 50 would be worth checking out. and if not then the sigma 85 would be a pretty solid upgrade

Maybe a 16-35 if you like weddings and parties indoors?

i do like the 16-35mm. is there a substantial difference between Mark I and II? how about against the older 17-35mm?

I've elected not to get a 50mm, and i ended up spending the cash on pocket wizards. at any rate, i'm still looking to get another lens.

I have had great success shooting events with the 24-105mm

For FF, I wouldn't be inclined to add a 50mm to what you already have. You might do better extending your range to wider or longer lenses. If you want to stick with primes. then either 24mm or 135mm (or both!) might be of interest.