It really depends on the fight and strategy that your group employs. 280 with 2 str + 3 vit accessories is not bad depending on your uptime during adds phase. One thing about t13 is the fact that if your dps do a lot of damage during adds phase, then all adds die really quickly and you end up waiting a long time for divebombs and teraflares, this drops your dps by a lot in an unmerged parse.

The best turn in FCoB to evaluate and compare OT dps for tanks is probably T10 imo.