I use Sapphire Trixx to downclock my memory to 150 Mhz which also increases hashrate due to tighter timings. 
how does downclocking the memory actually help? and, to me, this value seems insane!
are you sure you meant 150 Mhz ?I use Sapphire Trixx to downclock my memory to 150 Mhz which also increases hashrate due to tighter timings.
Using 15.7.1 and Trixx? Are You sure it's underclocked? Checked in Trixx card info or GPU-Z?
I'm absolutely certain, Trixx seems to be the only utility which allows you to do so without any hassle anyway. A wide variety of algorithms benefit from setting the memory to 150 Mhz [600 Mhz effective] such as Quark & Qubit which rely on latency rather than throughput. This sets your memory bus to a strap with tighter timings which will ultimately lower power consumption and heat and also allows for more overclocking headroom. To prove my point, I managed to yield 23 MH/s for Quark, a similar figure for Qubit and 37 MH/s Ethereum & 620 MH/s for Decred in dual mining mode on a 390x without rejected shares.
Has anyone tried Stilit's bios or any other modded bios for that matter on Ethereum?