Useful C4D Descriptions

 Beckman - very common type of reflection model

GGX - reflection model for brushed metal type materials

Dialectric - type of Fresnel model used in plastics

Conductor - type of Fresnel model used in metals

In C4D Physical Renderer (for Global Illumination), Quasi-Monte Carlo is what other renderers consider "brute force" (most accurate)

Irradiance Cache is not as accurate as QMC (Quasi-Monte Carlo) but it'll render faster.

PHYSICAL RENDER SETTINGS (rule of thumb)

SAMPLER

fixed - applies same sampling (computing) to every pixel (not too useful)

adaptive - smarter way of sampling based on scene complexity (best)

progressive - sampling done in "passes" where; passes are progressively "better" (good for previewing)

Sampling Subdivisions - 2

Shading Subdivisions (min) - 0

Shading Subdivisions (max) - 3

Shading Error Threshold - 3% (smaller is better, but slower)

You could set your Sampling Quality to "Automatic" where you control subdivisions with just the Threshold value and see how high of a value you can get away with. (higher value is faster) If later you need more sampling for, say, Ambient Occlusion, you then add that specifically.