well, I've got a CSt (2027's granddaddy), used to own a 2027, and own a UV7PWH. So...
Even piezos aside, they're really two totally different beasts. The (old style, non-AANJ) neck is definitely slimmer and more C-shaped than the 2027/CST (they feel pretty identical to me, off memory), and UV's have noticeably lighter/shorter frets than 2027's. They're both quite comfortable necks, it's jsut that the 2027/CST is quite a bit girth-ier - it fills your hand comfortably, while the UV melts under your hand.
Tonally, the ebony board and maple top brighten up the cST quite a bit, but on a 2027, you really need to match pickups to the body wood. a Tone Zone 7, what mine originally came with, in mahogany is just all midrange and not much else. A bright, slightly scooped pickup is ideal - the Evo7 kills in this one, and I've heard great things about the JB7.
Myself, if you have two 2027's, I'd sell one of them off and buy some other good seven string - a UV would be cool, as would a 1077/2077, a CT/8527, a JP7 or something to add a bit of variety to your collection.