Dear MDJAK,
Yep – that’s why I supplemented & added a liberating Fuji X100S (albeit with a fixed 35mm equivalent lens & Fuji EF-X20 small off camera flash) for very effective light-weight/fun activity. (still use the two 5DmkIII's & 1DmkIII for serious stuff though).
Wish the fundamental problem with DSLR’s that we all endure, that of uncomfortable weight & size for performance, was a simple fix!
Always hesitant to recommend bags, as they are such an individual preference, however given that you asked (& after carefully reading your criteria & with an implied bag ID of approx 500 cubic inches), here are four possible suggestions/options I have found effective for shoulder bags:
Think Tank CITY WALKER 20 [Mfr# 681]:
http://www.bhphotovideo.com …_Citywalker_20_Black.html
http://www.youtube.com/watch?v=VKHMoqmpSzs
(6:27 minute product video)
-I can highly recommend, (however, obviously everyone’s preference varies)
1=1 (using your math; => this bag keeps things light, with surprising capacity & simplicity!!)
-most comfortable shoulder strap of any bag I have ever owned during years of the bag iteration process (how many? like a females's age - don’t ask!)
-doesn’t need a Domke postal pad.
- very comfortable & contours to your body beautifully -subtle yet stylist in good taste
-great durable quality
- what I would describe as a “modern Domke”, without the bulk
[while the TT Retrospective series and DOMKE bags are nice I find them a bit too bulky & stiff. Even though, I highly respect moderator Jon’s lengthy experience & varied insight of photography items & subjects]
- bonus: no sweaty Spandex required!
-“scrunchable” (folds down flat) & very versatile for general travel (car or air), or family gatherings, events etc.
-fast access which you liked (you could probably be a contender for the title: “the fastest draw in the east”)
-a 5DmkIII or IDx either with mounted 70-200f2.8L mkII will fit upright tightly & certainly horizontally (but usually I have that combo out of bag, or just want to have it reachable in bag, or for transporting or for tucking camera away when going into restaurants, events, etc.).
Think Tank SPEEDRACER v2.0 [Mfr# 409]:
http://www.bhphotovideo.com …acer_V2_0_Black_Gray.html
-if want comfortable all-day wear & a true “shooting” bag (rather than just a carrying bag)
-nifty retractable waist belt (transferring load to waist, off shoulders)
-a bit big, but holds everything
Think Tank SPEEDFREAK v2.0 [Mfr# 406]:
http://www.bhphotovideo.com …reak_V2_0_Black_Gray.html
-if want comfortable all-day wear & a true “shooting” bag (rather than just a carrying bag)
-nifty retractable waist belt (transferring load to waist, off shoulders)
-caveat: with the TT SPEED FREAK v2.0, a mounted 70-200f2.8L mk II won’t fit vertically only just fits horizontally.
Lowepro Passport III Sling:
http://www.bhphotovideo.com …port_sling_iii_black.html
-for casual day explorations, travel etc. [Including weddings, if I am wearing a dress; I know not likely applicable in your case! When want a subtle photography profile)],
or if want to tote other stuff like miscellaneous travel items, snacks, a map, travel guide book, i-Pad 2, etc.
-a bit tight & not as comfortable as the other mentioned Think Tank bags
-“scrunchable” for travel
In SUMMARY…
For general use: Think Tank CITY WALKER 20 - black (as indicated, highly recommend)
For all-day walk around: Think Tank SPEEDRACER v2.0
Remember the general bag guideline - don’t carry more than 10-15% of your body weight, or your may be visiting your chiropractor or doctor for a fire-side chat!
Good luck in finding your elusive solution and HAPPY SHOOTING!!!!
Just one view…
Mary
P.S.
a.k.a. petite, but always camera ready in the west.
(not necessarily the “fastest in the west”; but I can hold my own to get the important photography elements of: light, composition & moment, thanks to my camera bags, which are based on real field-use & the help of so many friendly POTN users)