Had this situation today
An Incubi squad led by an archon already has a pain token (yay drugs) and assaults a marine squad containing a marine librarian. The archon kills the librarian at his int step with his husk blade and the unit gains its second pain token. Do the Incubi gain the benefit of furious charge when they strike the marine squad at their (lower) int step or not?
The unit does have two pain tokens and it did charge into assault in the current turn.