I use an f/4.0 Sigma 100-300, full frame size on my DSLR's.  It is not so heavy as the big one you have but does a very fine job.

The secret I learned about such lenses is practice, practice, practice.   I am  not so steady as in years past but had a lot of time shooting, rifles and handguns.  Practice was the key.  Steadiness in a lens is similar to rifle shooting except you cannot predict the place the shake will be when the  shutter is pulled as is possible with a rifle.

The same sort of hold, breath control, etc. seem to help a lot. 

Best wishes with the Bigma.    TomDart.