Oil windage losses in a high speed racing engine can be significant. BMW learned this the hard way, with their "laydown" turbo engine that they put in Brabham's BT-55 chassis.
Also, take a look at any engine designed to run at Indy. The oil scavenge pumps are about 20 times as large as the oil pressure pump, volume wise.
(And that doesn't include the mechanical air/oil separator in the system).