STR vs. VIT ... it's an interesting concept (no, DEX is not a consideration). Honestly, I don't think you can have enough of either currently.
If you're going to be staying below Titan HM, sure go all STR. You just outgear it at that point, so STR is the one that's useful.
Titan HM: you're going to get hit pretty hard, need lots of VIT. Coil t1: if you have enough VIT you can last to higher stacks on boss -- allows your group to use easier method. Coil t2: well it's possible to just die there. Can do with lesser, but more breathing room with full VIT. Coil t4: Healers can't concentrate just on you. You really need to both plan your cooldowns right and also as much VIT as possible.
In the harder areas STR still has a use. Ever had a good BLM with foe requiem decide to go burn? More tank dmg = more agro = more DPS they can do.
Personally, I'm full VIT with mega potion of strength, internal release, berserk, and a few STR jewelries in bag for those times when I need more agro.
Definitely get as much ilvl 90 armor (upgrades both str/vit) and HQ crafted jewelry as you can. Crafted jewelry is like you're trading 5 VIT for 10 STR as compared to ilvl 90 jewelry. Pretty good trade.