What am I meant to do
I need more performance than a 290x but I can't find a reasonable upgrade.
This is ludicrous.
I think the Vega 56 will be decent upgrade for you. It's going to be cheaper than the 1070. With the mining craze at the moment, you will still get pretty good money for 290x.
Combine the Vega 56 with a decent freesync screen and you have a high quality gaming rig.