I have the Sigma 120-300mm f/2.8 DG OS HSM Sports Lens and I love it. It is a fantastic lens. It was not cheap at $3500 bucks. It has been discontinued recently. I think the fact Canon lenses in this category cost more than the average consumer is willing to spend is why there never was a 150-600mm super zoom. I don't think Canon could make one for a grand.
From the outside the Siggy 120-300mm looks exactly like the Sigma 150-600mm f/5-6.3 DG OS HSM Sports Lens. It has the same basic construction. If you are considering one of these and still use the EF system, check out the used market as it should be a good buy used. Extremely well built lens,
EB
EOS 1DX and 1D Mk IV and several lenses!
