Note that at wind speeds above 18 kts, TF sails faster with the sails reefed to 150 square feet. Osprey will likely discover the same. Driving issue is foil drag cost to counter excessive righting moment.
In light air conditions the ability to generate (when there's more breeze) downforce from the windward foil will allow a larger rig and so could aid speed when in the light conditions.
However as you say, once breeze is enough to require downforce from the windward foil, the added sail area and the downforce seem counterproductive. While sail carrying power does increase as righting moment increases this way, there's twice as much (roughly) drag as usual for the added power.
(Twice, because the leeward foil's lift must also beyond sailing displacement by the same amount.)
Hard to see how added sail area requiring twice the drag per amount of sail force can yield more speed. Certainly the lift/drag ratio worsens as well.
I was having trouble seeing, in another thread, where speed limitation from lack of righting moment in the first place (center of gravity vs center of lift) could possibly be overcome by adding downforce: it continues to seem unlikely. I do see where the resulting ability to carry more sail means this can give more performance in light air while still being able to handle heavier air -- until losing downforce from whatever cause (cavitation, waves, a dynamic excursion, a control failure), then over you go quite rapidly.