I agree with Gamemako. It's definitely worthwhile to have a set for both: VIT and STR.

Conventional tanking wisdom tells us that survivability should always comes before damage. However, it should completely depend on the fight. As long as your HP is above a certain threshold (this # changes depending on the encounter and your role) to safely survive the mechanics, having more HP no longer really helps you (aside from Lustrate). Once you're above that Threshold and having that extra 450 HP no longer adds value, you might as well take the 45 STR and the Det/Acc/Crit. Tank DPS is still very significant, especially a Warrior's. Quickly killing adds and shortening the fight also relieves stress on the healers.

So, to answer Tano's question: It depends. The relative value of VIT to STR is completely dependent on what you're fighting. There are fights where I would never want to compromise my HP and there are fights where I wish I could wear Monk body pieces.