Hi

Can anyone point me to a good review of this lens?

I currently have a 5D mark II and a Canon 400/5.6. I primarily do aviation photography.

To get more reach than my current equipment, my options seem very limited. The new Canon super-telephotos are prohibitively expensive.

The Sigma 300/2.8 can be found in the UK for less than half the cost of the Canon equivalent. How does it compare? I dont expect it to be as good, but is it close? I'm thinking this lens with a 2x TC would give 600/5.6 when I need it and a high quality, fast 300mm the rest of the time.

Or would I be better off using a 1.4x TC with my 400mm and manual focussing?

Thanks!