The 6800xt is a great card for mining - check out our review and let us know your thoughts. Does it surpass the 5700xt?
The RX 5500 XT is the lowers in class of the 5000 series AMD cards. I have one of these and managed to get 27.5 MH/s at a reasonable wattage.
I have been busy looking forwards to the future and more sustainable energy options. If you are considering Solar for mining check out the post.
Lets talk about hashrate, this card looks to perform better on flux. Considering that Ethereum 2.0 is coming up this a decent use case for the card for this purpose.