I got my new Tamrac Velocity 7 today and did a test run to see how much gear I could get into it and I think it's going to work very well. I got my K10D with Tammy 28-75 attached, the DA55-300, the A50, and the Sunpak 383 flash into it. Tomorrow, I'll be getting the DA12-24, so that will most likely go in the place of the flash, or the 55-300, depending on where I'm going. If I want to take all 3 zooms, plus the flash, then I would see about getting the flash case that's a part of the MAS system, which would simply attach to one side of the bag. It's got a nice, slim profile which will help it stay out of the way when I'm moving around.
There's a butterfly garden in my area that I like to go to periodically that won't let anybody take in any camera bag at all. In that case, I have an regular size LLBean Touring Travel bag (
Touring Travel Bag: Shoulder Bags and Packs at L.L.Bean) that I use, which will hold camera and a couple of lenses, plus other personal effects. It doesn't look like a camera bag, so if you don't know what I have in there, you would assume it's a handbag and nothing more.
On the subject of museums, my husband and I went to the Florida Holocaust Museum in St. Petersburg and they wouldn't allow me to take my camera in, never mind use it.
As for the Lowepro Slingshot bag, the main reason I didn't consider it is that I think it's ugly. I'm not an extremely vain person as far as what I carry my camera around in, but I have my limits.
Heather