One answer from someone that actually owns a Super and a bunch from people that read it on the interwebz. If you already have an ECO why buy a CCO, regardless of caliber?
The Guardian gives you the advantage of a full size frame and magazines, 10+1 capacity in .38 Super. And, the Super is a fine self defense caliber, ammo is readily available and priced similarly to .45ACP. If you're smart you'll keep a stock on hand and buy extra when deals come along. Another advantage, as GoldieMI pointed out, is the easy conversion to 9mm, which let's you train with less expensive 9mm ammo and carry hotter Super loads. I have a custom 1991A1 Colt in .38 Super that is also fitted with 9mm and 9x23 Winchester barrels. I use 9mm for competition and training and either Super or 9x23 for carry. I keep a couple thousand rounds of 9mm on hand and at least a case each of Super and 9x23. That gives me the freedom to buy ammo when I want and the price is right, rather than worrying about what the local stores have in stock at inflated prices.
I've got a bunch of 1911s in .45 but my Super is one of the most versatile and fun pistols I have.
Oh, one more thing, I would never choose a Ruger 1911 over a Dan Wesson.