@BoggledBeagle single rank sticks are easier on the memory controller and can usually run with higher clocks and/or tighter timings. the record clocks on samsung b-die is usually single rank b-die.
dual rank sticks usually have double the amount of memory ICs that run in rank interleaving mode, which increases performance, but is more taxing on the memory controller and signal integrity, which generally leads to lower clocks and not as tight timings.
at the same clock and timings dual rank has quite a bit more throughput compared to single rank. due to the tight timings for lets say samsung b-die, single ranked ram can (not always will, but b-die certainly was) better in latency sensitive tasks when manually tuned.
for ryzen you want the memory at the infinity fabric clock sweet spot of the cpu before it drops out of 1:1 infinity fabric to dram clock ratio. for zen3 this is a ddr4 clock of 1800-1900mhz (ddr4 3600-3800) - which is quite easy to hit with friendly memory ICs such as hynix CJR even with dual rank. so the performance sweet spot for zen3 is ddr4 3600-3800 (depending on how stable your IF is) with two dual ranked ram sticks.
You can get the bank interleaving with 4 dimms of single ranked aswell, however that means you have to populate all 4 dimmslots. however it is better to run two sticks of dual ranked vs 4 sticks of single ranked because of signal integrity for the 2nd dimm - on modern boards the slots A1 and B1 are wired in daisy chain mode and not parallel, that means the signal quality is always worse on the A1 and B1 slots compared to the A2 and B2 slots - this is what is giving you a bad experience when fully populating a dualchannel 4 slot board.
so easy - just buy 2 sticks of dual ranked ram, right?
yeah no, because manufacturers never declare what type of ram you are getting. what used to be dualranked yesterday might be a different memory IC in single rank tomorrow with the same product name and specification.
whatever you plan on buying, you are at the mercy of RNGsus
