Recommendations on gear for Bird & Wild Life Photography

[anuritu]

I have been using Nikon D60 with a Sigma 120-400 f4.5-5.6 lens for bird and wildlife photography. Many a time I felt the reach was not sufficient, and so I bought a 2X multiplier to extend reach. Unfortunately, I am unable to use Autofocus with this combination.
I don't have sufficient funds to buy a faster ( f2.8 or f4 ) zoom lens of about 400mm.
Please advise me on what is an optimum solution?
What about the new Super-Zooms - Canon SX40HS-35X, and, Nikon P500-36X? How good is the IQ from these cameras, and their utility as travel cameras?
I'll appreciate your guidance to me.