Recessed screwdowns are about the same size as PSA/SGC slabs, maybe a little deeper. Should be fine in a penny sleeve in a climate controlled environment.
I bought a couple of the baseball card display frames at Michael's (regional decorator store) that had snap-tite style card holders with 1990s commons in them. They might be a tad shorter than PSA/SGC slabs, but are in the ballpark. Have about 50 of those holders I'm not using right now.
Here's a picture of those:
http://www.michaels.com/studio-decor.../10242171.html