I use just the 100-400 on my 7D and at brands for the BSB the light was awful to say the least and for the first time ever I stuck it on auto iso [cringe] but was quite surprised how well it worked out. Yes you can see the noise if you want to be really pedantic but for 'real world' use / prints it's fine (very little PP in this shot - sure with a bit of fettling you would never know)
example - under the tree's at clearways. 340mm iso 3200
Worth every penny in my book, I have covered a few events now since changing over to the canon and apart from putting the 24-105 on for a few paddock shot's the 100-400 hasn't come off the body.
.DAVID.