Those are different architectures, so you can't compare the hashrate and age in an apples to apples comparison. The HD 7900 series (and it's revised/upgraded generation after it) do quite well on Equihash, but they also consume allot of power by todays standards, so you need to keep electricity costs in mind when comparing to more current GPUs. As to the hashrate, 290 or so sounds just about right at stock settings for A RX 580. If you OC the core clocks a little you should get up over 300 sols.
yeah i even got 200 H/s with an Tahite LE i had lying around, but to the cost of a lot more electricity (200watt which is 1 sol per watt). so from an affciency point of view you are far better off in Hashes per Watt and therefore in income per card.