Your in exactly the same situation i was about 6 months ago, my 290 croaked, or at least i thought it did.... turns out it was the PSU leaving some strange carbon deposits on 2 of the 6 Pin PCIe connectors, i didn't realise it was doing that until the 970 started behaving the same way the 290 did, thats when i had a closer look at them both..... but anyway.
Having to spend the money i didn't want to get the 390 as they are similar GPU's, so given that i had to spend the money at least i was going to make it a change, so i got the GTX 970, very nice GPU but a side grade at best, even the 980 is no upgrade really, certainly not from a 290X and i'm just not comfortable spending £400+ on a GPU.
Anyway, I think for the sake of £40 get the 390X, you should gain a few percent, i don't think they are exactly identical, i think Crey may have a point.