old rule of thumb used to be 10psi for every 1000rpm it peaked at. They'll almost all pump enough from idle to about 2500rpm to be safe, but what the 'aim' is is for example if you redline/shift gears at 7000 rpm you'd want 70psi peak oil pressure. There's not a lot to be gained beyond around 80psi, infact it just strains the pump and costs a hp or two. It's generally only engines where the oil pump drive system is dodgy and prone to breaking (and then delivering zero oil pressure) that anyone aims below that rule of thumb. Off the top of my head, grey motor holdens, and hemi 6s - both of which tended to be fine with under 55psi oil pressure and higher rpm