White Fir Spring T-egg, cut or save?

I'd cut it.

For a specimen, you'd want a half egg with just the cut face polished. The rhyolite shell is one of the big things to ID that can differentiate one thunderegg locale from another, so collectors like to have the intact shell surface.

For a cab, you'll probably want to chip off the rhyolite. It is too porous and crumbly in White Fir to attempt to preserve it as part of your cab design. If you preserve as much of the jasper as possible, I see a silhouette of a girl with a pony tail.