I have (had) springs on my 2015 bird pups. Hated them, replaced with high density foam.
I frequently anchor my thumb on the pickups, and when equipped with Springs the pup moves all over the place, drives me nutz. With good high density foam (the type you can get from the hardware store for weather stripping) I can get the pups up nice and high and rock solid.
If you use ordinary foam rubber it will be too squishy, try some of the adhesive backed weather stripping type foam, it works great. BTW - I keep my pups up as close to the strings as I can get them without the strings touching when depressed at the last fret (exception being the 2015 bird, it's a totally different beast when it comes to pup height).