Titankid

What kind of lenses do you have ? EF-S (Crop Lenses) or mostly EF (Full Frame) glass? If you have mostly EF-S glass then the 6D MKll is pretty much a no go as Canon's FF DSLR's are not compatible with their EF-S lenses.
 
Also what kind of Photography do you do right now? A lot portraits and landscapes or do you like to take advantage of the 80D's 7FPS and pretty good tracking for action and wildlife? If you don't do action/wildlife then save up for the EOS-R w/ its 30 MP sensor as its one of the 3 Canon Bodies that has an actually noticeable increase in resolution over the 80D and the cheapest @ 2300 USD + with the EF-RF adapter + you can still use EF-S glass something Canon's FF DSLR's can't do.
 

I am a bit displeased with the 6d2's AF system, its always been a matter of contention with the 6d tbh, but, they fitted the admittedly excellent for APS-C 45 AF point system on it, which makes a very poor coverage for a FF sensor. 
 
I would really consider going for an eos r vs the 6d2, since the price can't be that much off used, I've found loads of bundles on ebay with the RF 24-105mm for under £2000 for some time now. The rp might also be a choice, although I hate they didn't go with the LP6N battery making its battery life suck and me having to buy new batteries. 
 
Now none of them are there yet, I think there's stuff they need to fix, but if you can save up for a while and buy an r instead, I think it would be worth it for a multitude of reasons, you'll get 4k, even at an APS-C equivalent sensor using the crop, but I imagine you have EF-S lenses for that, the AF system is great, you get a higher resolution sensor and I think newer processor and RF, EF and EF-S compatibility. 

Consider what lenses do you have and use most (primes or zoom, L or consumer) and how...
 
Be aware that full frame + higher density will reveal the weaknesses of zooms and/or non primes. (Esp wides and teles)
 
Plus if for example you mostly use long primes or long ends of zoom you'll "lose" a few mm of "zoom"(actaually, crop)  by getting more of the frame; of course you could crop but then the extra pixels and larger sensor are sort of wasted.