CGA's aren't nearly 4 inches thick any more. Most times you probably wouldn't be able to tell the difference from what you're looking for (good floating non-cga) from an actual "wakeboarding" CGA vest. So why not just go to a CGA?
What it comes down to IMO is you can't have a t-shirt float 120 pounds of muscle. It just doesn't work.
More on topic, just go try some on if you can. Sounds like you're in an area where you have a shop close by, too. (lucky dog