I have been quite happy with Sigma 150-500 OS ... mostly used it for birds, and small desert wild life as well as the birds at our local zoo. But now I am using it less and less and our local zoo has also closed for renovation and will remain closed for the next 3 to 5 years so I don't see much use for it in the next few years and lugging this big lens is getting to me for those very rare occasions when I need the reach.
So, I'm thinking of selling the Sigma 150-500 OS and buying the Canon EF 2x Extender III (to be used with my EF 70-200 f/2.8 L IS II on 5D MK III).
I am aware that using the extender slows down the AF of 70-200, but does it end up being slower than the sigma 150-500 OS?
5D MK III, 16-35/2.8 L II, 24-70/2.8 VC, 24-105/4 L IS, 70-200/2.8 L IS II, 100/2.8 L IS, 40/2.8, 50/1.4, 85/1.8, 150-500 OS, 600EX-RTx2, ST-E3-RT, Rokinon 24/3.5 T-S, D7100+18-300 VR, YN568EX, 055CXPRO4+468MGRC2, 190CXPRO4+322RC2, Gorillapod Focus+496RC2, CamRanger, B+W filters, Konova K3/31.5 etc