ok now I am getting confused a bit.
If I was to go for the high dex route then surely I should have Toughness and FCB to HP to balance out the lack of HP from CON?
Also since my CON is lower I am not going to hap a mass amount of TEMP HP anyways so Raging vitality doesn't really matter as I could just drop my rage if things get messy?
Also, I think Raging Vitality is more beneficial for those that don't take Superstitious as you can't heal when raging and if you are using RV then as soon as you drop Rage you are definitely dead. Seems like a Kamikaze approach to a lose lose situation.
Most characters that are ever built by point buy have 12 to 14 con, just because it's an important stat, but not the stat that makes your character shine, it's just necessary to stay alive. 13 Con, or 14 at level 4 is about as good as you can expect. D12 HD + Con 14 is a respectable amount of HP
Now, there's a solid case for Toughness and Con 16 (although I would stick with the Human FCB no matter what.) However, in Pathfinder, when given the choice between being harder to kill vs more combat options/killing power, I usually choose the latter.
High dex opens up new options like archery and reach (combat reflexes) And the initiative, reflex, and AC boost are subtle ways of increasing your HP. (Reflex so you take half damage, AC so you take no damage, initiative so you kill them before they kill you.)
And instead of toughness, I'd sooner start climbing feat trees, save feats for rage powers and so on.
But again, 20 str 14 dex (at level 4) and 16 con is an exceptional barbarian as well. And a Barbarian with Toughness is certainly less likely to die from damage. It's all personal preference.