Hi there
Crypto n00b here 
I have a quick question that puzzles me.
I’m my PC, I have an R7 260x 2GB and an RX 460 4GB.
Using Claymore’s ZCash AMD GPU Miner, my weaker 260x is getting about 105 H/s, but the more powerful RX 460 is hashing at about 95 H/s
Now I believe the better card should be at least 30% more powerful, indeed when mining Ethereum it shows a hashrate that’s double. So can anyone have any thoughts about what’s going on with my Zcash?
Claymore tells you why this happens in his instructions to set up cards “For 4xx cards (Polaris) Crimson 16.12.2 is recommended.”
I don’t want to get into semantics, but saying something is ‘recommended’ is a long way away from telling someone that their hashrate might be affected by up to 50% 
So, you think if I roll back to 16.12.2, all will be solved?
Really?
Modern drivers are THAT bad at mining for AMD?
In my 12+ months of experience, it’s not that I think, It is that I know.
and no it will not because rolling back will affect the other gpu, but you can try and see and prove it to yourself
I really hate messing about with drivers 
Still… I’ll give it a whirl.
Hopefully the Hashrate increase on the ‘good’ card will be larger than any Hashrate decrease on the ‘bad’ card.
Well, I tried what you suggested and it was a disaster.
Not only did the 16.12.2 drivers lose me about 50% of my total Hashrate, but when I tried to put things back to normal, something terrible happened with my PC and I kid you not, it took 4 hours to fix. from display drivers crashing to numerous BSODs
Now my PC is back to how it was and I’m still hashing at a lower rate than before.
Weird… I’m on the same drivers that I was on before messing around and I’m hashing about 20% slower
The moral of the story… try to get more than one point of view before you go messing about with your hardware 
the reason for the bad performance you are getting now is a conflict of / stuck driver.
Run DDU in safe mode, uninstall the drivers, do a clean install of whatever driver you want to use