My oil cooler is stock 20b, never seen a 13b oil cooler so can't really compare. but I'd guess mazda would use same brand.
To verify if the cooler is restrictive, wouldn't a oil pressure drop be noticeable once the thermostat closed? with the sensor after cooler on filter pad. I cant say I've noticed it, but will look closer next run.
I've been reluctant to change the oil cooler up to now, as none of the suppliers seem to be able to offer flow curves so finding it a bit hard to compare.
I'll see if I can borrow a hydraulic test set from a shop here. If I place it at the oil out port and get pressure and flow there I'll have a much better picture of what's happening now that I got your pump flows.
Lynn, from your explanation, seems to confirm my gut feel that I need to have that external OCV, to cool all the oil being pumped. but maybe I could use a oil to coolant exchanger to even up the system capacities.