1) yes, that is true.  2) I installed pure Display Driver, no AMD settings or anything else (ASUS GPU Tweak works better than AMD Wattman for me). 3) all answers on screenshot of my settings and mining result. My card is ASUS ROG STRIX Radeon RX Vega64 8GB OC , samsung memory.

I tried the 18.5.1   driver on Vega64. Cast XMR doesn't show any difference to the previous 18.4.1 (same 2020-2040 H\s on v7 and 1530-1540 H\s on Heavy), but the SRB-miner 15.5 with new driver is MUCH better: v7 before was 1950 H\s, now 2070 H\s; heavy 1430 H\s before, now  1680.  Developers of CAST XMR should release the next version with improved hashrate if they want to have their 1.5% dev.fee. As for now SUMO mining on SRB-miner 15.5 (0.85% dev fee) looks more profitable for miners. And in spite of announced nicehash support Isince 0.9.x of CAST XMR I always have 100% reject. This have to be fixed.

Can't keep my Frontier at 2100. In a minute it goes right down to 1700/1800 range.

Already tried with max min fan speed. Something is missing me.

For now all I'm doing is setting the memory to 1100, the memory voltage to 905mV and running 2 threads of 2016 intensity.
All the core values are still at default.

What am I missing?