"poison potency" is an outright +15% damage to ALL of your charges.
blade tempo is an amazing CD, over the course of the fight its 3.75% damage on a tank and spank, but on most actual boss fights there are prefered time to DPS harder.
while dropping both of those you picked up:
the 5th point in improved det, increasing an ability that does about 7.5% of your dps by 4% (from 120% to 125%), that would be what, a .3% dps increase? ( 1/3rd of 1%) as opposed to the 3.75% of blade tempo.
and 9% dex, which would be pretty darn nice to have. i have 719 dex unbuffed in decent gear, 850ish raid buff sound likely? using rough numbers, 76 crit and 38 atk power gain, which, once again, would be nice to have. but if you take off ALL of your gear short of weapons, you lose 30% of your damage (on a dummy). stats arent as huge a boost in this game as in most.
poison potency is a 15% increase on 65% of your damage (spike and shrap) or 9.75% increase in DPS.
i very easily could be wrong, but i couldnt see it truely being a higher DPS build.