Well you are not alone. My old i7 980x cant cut it any more either. I also run out of memory despite having 12 gb.
The sweetspot memory for zen 3 would be 3600 mhz cl 16-16-16 running dual rank per memory channel (means 2 x 16 gb or 4 x 8 GB module for a 32 gb kit for an axsemple). But you can be lucky infinity fabric can handle up to 4000 mhz memory, but no garantee for it. I chose to go for 3600 mhz CL14 memory for my system. But values for money, CL14 is not the solution. I chose CL14 cause I wanted the no compromise experience. CL14 is however also fairly expensive.
So my recommendation will be 3600 mhz cl16-16-16 running dual rank per memory channel. Then you get the most out of Zen 3 with out paying to much on memory.
For ideas to memory. These two kits.
QVL (Qualified Vendor List) for F4-3600C16D-32GTZR-(EOL). Find compatible motherboard or hardware for this product.
www.gskill.com
A cheaper alternative, but also have loser timings.
Featuring the award-winning Trident Z heatspreader design, the Trident Z RGB memory series combines vivid RGB lighting with awesome DDR4 DRAM performance.
www.gskill.com