Optimize rendering for performance or memory

hello: running 64 GB RAM with Seperate scratch, media, and project HDs, NVIDIA GEForce RTX 2080 Super; and Intel i9-9900K 2.6GHz

• for some reason: i get a slugging adobe premier experinence. 
• I am using 4K files; and, sometimes use proxies. 
• Though, my 4Ks are only about 15 mins long;
• I do use some MOGRTs and the like.

any tips/pearls on how to get this to be less sluggish would be greatly appreciated.

under Optimize Rendering:

should I have it for "Performance" or "Memory"

thanks