I use the
Tamrac 5371 for my EOS-20D, EF 24-105 F4L IS, EFS 10-22, battery charger, two batteries, two CF cards, lens caps, EOS-20D manuals, and cleaning kit (zip-lock bag with a bulb air blower, Zeiss lens spray, and two lens-safe cloths). With all of this, the bag is pretty full. You might want to consider the 5273 as an alternative. But it's light-weight, a backpack, and small.
And RE: the 17-85 IS vs. Sigma 17-70. Have you considered the Tamron 17-50 F2.8 or Canon 17-55 F2.8IS? Both are getting rave reviews.