Does the Proofide make it less slippery? I went for a short ride to test the saddle position and everything felt fine except for the slipperiness factor.
On a dried-out saddle with a rough surface it makes it more slippery, since it adds oil and enables the leather to flex. Then your butt pressure and motion polish it.
On a newer one, I don't think it makes a lot of difference.
If you're slipping forward, try angling the saddle nose up just a tiny scootch at a time. It could also be that "forward" is where your pedaling technique is best, and your body is finding where it wants to be. If you think this is what's happening, try sliding the saddle forward to put the wide part of the saddle under your 'bones AFTER you slip forward. You mihgt not need to be in a KOPS knee position.
Road Fan