My wife has a Lowepro Slingshot 200, and I've been envious, but it is not big enough for my gear. This last weekend I got the new Slingshot 300. What a beautiful design.
It holds my 1D2 with the 100-400 attached (lens hood reversed) in the center compartment. In the other compartments I have the 16-35, 28-135 (reversed lenshoods) and 15mm fisheye, as well as my 500EX flash.
There is also a roomy compartment for other stuff. In addition to the strap that holds the bag in place there is a padded waist strap that distributes the weight and stabilizes the bag.
Just about everything that fit in my Reporter Stealth 650 fits nicely into the Slingshot. Access to thethree lenses I use most often is fast and easy.
I think the design of the bag is ingenious, and when accessing the gear, it slides around to mid-chest level with a cover that opens outward.
Here's a link to see the bag:
http://www.bhphotovideo.com/bnh/controller/home;jsessionid=F0y2QmkxQv!1927855174!116527590233 9?ci=1&sb=ps&pn=1&sq=desc&InitialSearch=yes&O=RootPage.jsp&A=search&Q=*&bhs=t&shs=slingshot+300&image.x=0&image.y=0