What's the deal about 150mm - there is nary a zoom lens with that as the top setting, 'cept their recent 35-150 of course.
At 21cm long and 1.7kg this 150-500 f5-6.7 is a big lens.
I'm not a wildlife shooter, but I'd be much more interested in a 13cm long, 588g, 105-450mm f6-8.4 lens (the Fuji 70-300 f4-5.6) ;-)