full groove main bearings oil pressure ?

There's no use having a high volume oil pump without the increased capacity of the pan.
If you had a high volume oil pump with say a 4 quart pan, you could easily suck the pan dry if you were doing a high R.P.M. charge for a prolonged period of time.
I lost a couple of rod bearings back in the day while i was top ending the 383 in my '69 Super Bee because of this. It had a stock 383 and a 4 quart pan off of a Newport in it.
Volume versus drain back should go hand in hand as well as considering the capacity.
High capacity pans and windage trays were put on all of the high performance and severe duty engines back in the day for a reason. (Industrial and motor home)
When i built the 440 for it, it got the 6 quart pan and Hemi pickup with a high volume and high pressure spring oil pump with the windage tray. The bearings were set at .002 with fully grooved mains and regular Clevite 77 rod bearings, and the pressure was 60 psi cold and 40 psi hot at idle with a max of 70 psi at 6,000 rpm using 10w 30 oil. I had no problems with it and i drove it for 10 years and raced it a lot. The engine was getting kinda tired by then, but the oiling system never changed.
These days, adding synthetic oil to the mix makes it even better.