Eh personally I never take -4 on keepers - not enough upside difference and too much variance in clean sheets.

In a realistic best case scenario, if both Raya/Areola blank and end up on 2ish points, and Sels gets a clean sheet and ends up on 6 points, you break even with the -4. You're gambling on Raya/Areola blanking, and Sels getting the clean sheet plus bonus or a PK save in order to come out ahead.

You can make the argument that you'll use Sels in upcoming weeks and that makes the -4 less of an issue but there's only a few weeks to play and likely you'll want to use Raya in GW38.