Hi, Gary. Yes, the Bigma has occured to me as well as the Sigma 150-500. But we're talking about essentially $1000 lenses, which is out of the question for me, at least right now.
I wish that 135-400(ish) lens that has been on Pentax's roadmap for a while would finally be introduced. But even that would only take me out as far as my Panasonic 100-600 and it'll probably be $1000, given Pentax's modern pricing.
That's why your Fuji HS50 has caught my attention. For $350, it punches above its weight as does the Canon SX50. I'm sure I can still get a fair amount with the DA 55-500. But a good bridge camera might be worth it for the real reach - at least for a while.