Dual Wield Trait Tier Testing:

Quote Originally Posted by DNC DW3/4
Level 79, 2x Bronze Knife = 4.7TP/hit (DW3)
Level 80, 2x Bronze Knife = 4.6 TP/hit (DW4)
Quote Originally Posted by DNC DW2/3
Level 59, 2x Bronze Knife = 4.8TP/hit (DW2)
Level 60, 2x Bronze Knife = 4.7 TP/hit (DW3)
Quote Originally Posted by DNC DW1/2
Level 39, 2x Bronze Knife = 4.9TP/hit (DW1)
Level 40, 2x Bronze Knife = 4.8 TP/hit (DW2)
Quote Originally Posted by THF DW1/2
Level 88, 2x Bronze Knife = 4.9TP/hit (DW1)
Level 89, 2x Bronze Knife = 4.9 TP/hit (DW1)
Level 90, 2x Bronze Knife = 4.8 TP/hit (DW2)
I also tested, and DNC doesn't get another level of DW by 95. THF and DNC may each get one more tier of DW at 99, similar to Monk's level 75 Martial Arts trait, but I wouldn't bet my life on it.

Additional notes: At level 80, Dancer still has Tactical Parry I.