I've recorded and toured with the Keystone drums, which are the predecessor to the Classic Oak (same shell.) I like the punchy attack. When they first appeared at NAMM, there was one new Keystone kit in the booth, and I could always tell just by listening when that kit was being played.
There are a few differences between the Keystones, Keystone-X, and Classic Oak. The Keystones had the Epic lug and were available with wrap finishes only. The Keystone-X came with Classic lugs and were available in black or white finishes painted directly on the oak. Classic Oaks are available in stained oak finishes (which look great!) and the name was introduced because Keystone didn't indicate the line's oak shells (in the way Classic Maple, Legacy Maple and Legacy Mahogany indicate what those shells are.)
There was a Whiskey finish Classic Oak kit at the last NAMM show and it was lovely and sounded great!