I used an 80D and Sigma 150-600C last May in Yellowstone. I think you'll like the combo. I'm hoping to go back this May. I haven't really played with video yet, but I'm hoping to shoot more this year - I like the idea of 600mm with the 3x@1080p.
I have an album on my smugmug page for Yellowstone (link is in my signature). Most of the wildlife shots are with the combo.
Congrats on getting to go to Yellowstone!
edit: One thing I learned about video last year was if you are using a tripod, be sure to turn off your OS on the lens. I know it's common knowledge, but I didn't think about it and the OS caused shaking that ruined some videos. Rookie Mistake!
Thanks! I am really looking forward to the trip. Will be at fishing Bridge from May 7th to 21st. This will be our 6th trip out. Last trip was in Sept of 2015, had the 150-600 but only a T2i for the body. Took some great shots with that combo. Purchased the 70d (Canon Refurb) in Dec of 2015 thinking that I could get a year in practicing with it. One of the biggest things I did not like was having to switch lens when mainly out for landscape and along comes some wildlife that I want to shoot. Lost a lot of opportunities while doing the switch and then ready but the wildlife was gone! So, while planning for this upcoming trip I decided to get the 80D. I purchased through Canon refurb site at a great deal so I am quite happy now. Nothing like having both cameras with you and just having to reach for the 150-600 and start shooting! I hardly do any video but it is nice to have that available with the 600 on it! Here is one of the first pics I got when I finnished with the AFMA on the 150-600.