What's the minimum I should upgrade to from Vega 56?

I have a Sapphire pulse vega 56 and I'm thinking of an upgrade. I'm on a budget however, trying to stay under 100 euros. I was thinking of used gtx 1080 strix for 80 euros, but would it be worth it? I think I can get 60-70 euros back from the Vega 56.

(Btw, I can't flash the Vega 64 bios to this card)