This was my issue as well - finding myself strolling around the park/lake and downtown for hours at a time. I got the Lowepro Stealth Report 550 AW thinking it would fill the bill. It did not. Great bag but I found that anything I *carried* and put down to shoot was a major hindrance. After a few bags - and some more research - I opted to go with a Think Tank Speed Freak (www.thinktankphoto.com
) and a lens case/strobe case on the side. It is comfortable, has top zipper to work out of, doesn't have to be sat down to get gear out of, is not too large (there is a larger and smaller waist bag...this is the Goldilocks - not too big and not too small) and very well built - also a built in rain cover. The waist bag system is a winner for me (just my thought) - the shoulder bag (Stealth Reporter) and backpack (I have a Canon backpack) both need to be taken off/sat down to do gear changes. I can't really comment on the Slingshot. When I wander about - for hours at a time - I have my Rebel XT w/ grip, 17-85 w/hood, 70-200 F4L IS w/hood, Speedlite 430 EX, pens, moo cards, filters and a Kata rain cover in a side pocket...with just a little miscellany left over...Really comfy system and easy to work with. Hope it helps and hope you find your solution.