Nick
I believe this is the first time I have ever thought to disagree with you, even if not completely.
I don't know about a 1000 pound increase but I would not rule it out. My experience has only been with the UH-1H which I flew before, and after, strakes and fast-fin were added. I was doing fires and would run out of pedal at 48 pounds of torque (at altitude) so there were often times where I came out of the dipsite doing hover turns until I could get some speed to get the tail back in line.
After the strakes and fast-fin were added, I never ran out of tail rotor and as a result could lift a bit smoother using less pedal. That was operating at 10 000 feet in Utah. If the tail rotor is using less power, then there is more available to the main rotor so it should be able to lift more. They do make a difference and the 1000 pounds increase is not beyond the realms of credibility. I suspect more like 600 pounds but I have nothing to back that up with except what I felt in the helicopter.