I wrote a guide trying to accurately quantify how various stats compared in an SA/TA set. However, I feel that if we're talking inside of abyssea, so many things have changed that I'm not so sure it's very accurate anymore. I never did quantify how much a single piece of "increased critical damage x%" did. I only did some napkin math on it once to compare tumbler trunks to sa/ta modified desultor tassets. I reached my conclusion but I don't remember how I got there. It wouldn't be too difficult to quantify it in the terms of the previous guide, but given how much the game has changed, I'm reluctant to ><.
The str/dex mantle looks really good, but according to the guide I did at least, it's about equal to a Forager's, where Cerb+1 and chargers mantle or the new aseling mantle (sp?) are better. However, if you have Razed Ruins and no +attack or +str atma, I have a feeling that the attack mantles would be even better. If you wanted to use my probably outdated guide (http://shamayaasura.livejournal.com/7505.html),
playing with some math it looks like each point of % crit would be worth a little more than 1.28 dex. So its value in the table would probably be listed as a little more than 3.30.