I have posted in several threads about possibility of raising UCLK on ryzen(it is listed in OC & ryzen master section of AMDS official website.) However, I have yet to hear a response if its hidden, or not currently present in AMD bios options for mobos.
I believe these 10% deficits after SMT modifications can be reduced to zero in comparison to the 6900k if UCLK can be raised to at least 2.8ghz...if not higher to say 3.2 or 3.3(which is the highest frequency achieveable on normal core before voltage bumps.)
Currently ryzen with 2400mhz memory the IMC is 1200mhz...with 3200mhz memory IMC is 1600...Highest i saw on non LN2 world records was 4.1allcore with 1800mhz uncore....thus they mustve had 3600mhz memory. If this can be decoupled, or at least forced into 2x mode(aka full memory speed rather than half) I honestly believe all of ryzens deficits sub AVX differences(Deficits of which im not sure even exist in benchmarks despite their smaller width) will disappear completely. In fact, due to its faster memory fabric, better smt, lower loss data conversions, and high clocks on base, turbo and with xfr for 1800x, I would expect it to outperform the 6900k by around at least 5% when all bios/windows updates are solved.
However, no one has responded to my comments, so either someone has read my messages and is currently testing, or my messages are being ignored.