Fast-Access Bag for a Monster Lens... On a Petite Woman

I'm in search of a new fast-access bag. I'm adding a Sigma 150-500 "Bigmos" to my kit (9.9" long, 86mm front thread - and this is before the reversed hood - the specs show a 94.77mm (3.7") full diameter). While I've seen several threads which address whether a 100-400 fits in a particular bag, such as the Primus, Flipside 200, Fastpack 250 and Slingshot 200 or 300, I'm now trying to find a fast-access bag which can take this heavy monster.

Since I shoot mostly wildlife with some landscape, my typical kit will be:

Gripped Canon 400D
Sigma 150-500 OS
Sigma 18-200 OS
Sigma 10-20 (I never set out to have a mostly Sigma kit, but it sure seems to have happened, doesn't it? At least my UW stuff is Canon and Tokina).
2 CP Filters
Misc. cleaning supplies
CF cards, batteries, etc.
Camera Storm Jacket

I've had all the above, though with a 100-400 (which is 2" shorter) instead of the 150-500, in a Slingshot 200, and it fit snugly, but I found I wasn't comfortable with the Slingshot style - I think I'd prefer the stability of two shoulder straps. Complicating things, I'm under 5 feet tall, and a "curvy" woman, so the bag needs to be relatively shorter so it's not bouncing around on my hips while I'm walking. So a shorter, wider bag would probably be better. Something that will comfortably fit this kit, but also distribute the weight of the Bigmos.

And yes, I do prefer a fast access bag for exactly the reason that I'm generally making lens changes outside with no convenient place to rest the bag easily. However, I'm not trying to have a bag which would accommodate the Bigmos mounted on the body, which should make things a bit easier. I would, however, like to be able to access the Bigmos for a lens change fairly easily.

Does the Primus, Faspack or Flipside suit my needs? Anything from Kata or another manufacturer I've not considered? Help!

Just updating here: Thanks to a very helpful POTN'er, I'm now seriously looking at the ThinkTank Rotation 360. I'd seen and tried it on briefly about a month ago, but it was before I'd gone with the Bigmos, and I'd forgotten all about it. It may be perfect for my needs, but with an accessory lens case.

Lowepro suggests the Flipside 300, but that just seems terribly long for me. I'd have to try that in person to see how it rides.

Anyone else with input? I appreciate information, here or through PM

I have Rotation 360, Flipside 300 and Primus. I recommend Flipside 300. My daughter is 5' 2" and it fits her fine and she says it's very comfortable even when loaded to 20lbs. However, I find shoulder padding isn't really adequate for long distance walking. It is my go to bag when I'm using 100-400. One of prime advantage of Flipside compared to Fastpack is that you can change lenses without taking the bag off. I've never found sling type bags comfortable when loaded with more than body and a lens.