If you want light and simple, try one of these
http://www.thinktankphoto.com/ttp_product_DgtlHlstr.php
I have the Think Tank holster 30. The 70-200mm with the hood attached and mounted on the K7 fits into the bag, ready to be quickly removed, pop the cap and fire away. I also carry the DA40mm in the side pocket and a 1.5xTC in my pants pocket. This gives me quite a bit of flexibility. For those that go biking, this bag offers protection when carried in panniers and is still very accessible. Another lens fit combo is the DA 12-24mm at the bottom of the bag, the f*300mm mounted on the camera inserted above it (no hood extended) and the DA40mm in the side pocket plus an xtra battery.