in high performance setups is significant and can cause all sorts of problems as well as rob hp. This problem can be even worse in turbo motors. Remember, the pcv system was designed for stock hp levels and in some cases isn't adequate even then. I've built non turbo street engines that would blow the dipstick out because of this pressure. That's why you'll find guys that run vented setups with -8,-10, or -12 AN fittings plumbed to a sump breather to vent off the pressure band collect the oil that's left behind. Some guys even use a drain back from the bottom of the tank that is routed back into the oil pan to increase efficiency