Remember that if you're maintaining something crazy like 1600 DPS with a rogue with salv on you will have 1600*0.8*0.7=896 tps... So 1500 tps for a tank is far from nescessary. For a mage it's only 0.9 instead of 0.8 but you probably aren't gonna get 1600 dps either ;p of cousre these numbers are just guestimations but I don't see how you can realistically do enough DPS to pull aggro from a good tank if you have salv on. If you don't have salv, well, recruit more pallies... 2 blessings is a minimum for raiding and 3 is optimal
Shadow priest is the only DPS class that can reach insane TPS values and that's only when you're getting full effect (or close to full effect) of VE while having awesome DPS. I hadn't seen a fight though where VE is actually doing full time healing - shadow priests are always #1 on the overhealing meters by far.