Help with a lens?

Hey All, thinking adout buying a new lens for use on a Canon 40D at airshows ect. I Have a 70-300 IS Lens but want something a bit longer. I did have my eye on the 100-400mm f4.5-5.6 L IS USM, but with the fall of the $ the price has shot up by about 30% 😡 kinda putting it outa my price range.

I’ve had a look for an alternative and i think i’m set on the Sigma 150-500mm f5.6-6.3 APO OS HSM. Has anyone any experiance of this lens or maybe suggest a sutible alternative?