Thats nice results given the fact that you started from 76ns. With what DRAM voltage is this?
Memory bandwidth (GB/s) is also up. As other stated you dont want the MCLK/FCLK/UCLK to be decoupled as this is giving a significant latency penalty. Keep them all at 1800MHz.
There is always room for improvement, but from this point on the gains will be minimal.
If you feel like it you can try:
16-18-18-18-38 (first 5 of ZenTimings)
tRC: 56 (18+38)
tFAW: 28 (tRRDS x4)
tRFC: 456 (tRC x8+8)
All timings are related (add, subtract or multiply) to each other, and none of them are random numbers.
GDM (GearDownMode) Enabled as you have, its like having the Cmd2T to 1.5T instead of 1T. Though in order to disabled it you may have to increase DRAM voltage. It may not worth it for the improvement return.
----------------------------------------------------
As for Corsair RAM it all depends on the part number of sticks. Z series are the only "guaranteed" that will work with Ryzen and others may work or may not.
I learnt something the other day from someone I know at Corsairs that's involved in their memory products. Apparently some LPX kits are suitable for AMD use, but Corsair doesn't really mark them specifically as such on the packaging. There is some information on their website, but the key thing...
www.techpowerup.com