I’m an old fashioned enthusiast to me it doesn’t matter how powerful the hardware is I want to maximise the potential and put my own stamp on it, modern hardware doesn’t allow you to do that, hell, modern hardware doesn’t even allow you to remove a cooler for a proper maintenance clean with those absurd “warranty void if removed” stickers over a screw. Fortunately such things won’t stop me as I have the means to remove them without any signs but for most other people that’s just not possible.
With the limited bandwidth you have you probably wouldn’t even lose much, dropping to 1250MHz on the GPU. Given the power restraints you have you’d be much better served optimising bandwidth at stock speeds to keep all voltages as low as possible you really won’t be losing anything because the important thing is the bandwidth efficiency itself. Polaris is bandwidth starved, not frequency starved. Even when I ran an RX590 @ 1.6GHz / 9GHz with highly optimised Micron timings that netted me absolutely nothing outside of margin of error compared to one of my RX580s @ 1.4GHz / 8.8GHz with highly optimised Hynix timings. Without a memory upgrade to GDDR5X at those points Polaris simply had no more to give I’d think I was also bumping up against core performance limits too there’s only so much more you can get out of 2304 shaders and 36CUs.
None the less though a fully optimised 580/90 will give a Vega56 a run for it’s money a lot of the time and a GTX1070 too, that’s not bad at all even now it still firmly puts Polaris cards in potent 1080p territory.