Well, Just went back to mining in my Python 192T Cargo as I like it only in short and sweet blocks.
In two days on and off I have almost refilled my Raw Mats entirely, in addition to the CG stuff required - I was getting very low on raw mats anyways with the war effort and CZ's etc, so it is a double bonus in that respect. There is the bonus of a raw material trader at Utley Hub to trade the mats up and reset.
BTW I went to a Pristine Metal Rich on way here and then after delivery, went to CG system Kokoller AB1 which is only Metal Rich Major Reserves and there is almost no difference, if any, in the time taken to fill 192T (I only mine anything over 15%).
You don't even need PWS/Core/Subsurface, just prospect and mine with 2D and 1D (long range pre-engineered) lasers and deliver quickly.
You also get Osmium in Metal Rich as a bonus in some asteroids. I have found some asteroids have all 3 (Bert, Colt, and Pras)
There is Platinum in Metal Rich but only in Cores, not surface.