I don't think you can buy a better bag for what you want to carry than the
Domke F-8 Small Shoulder Bag. It's like they made it specifically for Pentax DSLRs and their small primes.
At the bottom of the main compartment, I've made a divider which divides the bottom 1/2 of the bag into two halves. I can fit two smaller primes such as any of the Ltds or my FA 50/1.7 in either half. That's 4 primes in the bottom. I the photo below you can see the DA15, 21, 35 & 70 in the bottom. In the photo I'm using the
Op/tech Double Lens Mount Cap to keep two lenses attached to one another, but I'll often just put the two lenses with their rear caps pointed toward one another as there'll be no scuffing of the lens bodies that way either. If I'd rather, I can put two primes in one half and a single longer lens, such as the DFA100macro, DA18-135 or FA135/2.8 in the other half.
Separating the top half from the bottom half, I've put a flap that quickly folds up and out of the way to allow access the bottom half. It doesn't completely cover the bottom half, but the camera up top has never bumped the lenses below.
In the top half I put my camera (K5) with a lens attached. With the hood reversed I can fit any of the larger lenses mentioned above in the top half. You can see my DA18-135 mounted in the photo below. I can even get the DA12-24 with hood reversed in there but that's about the biggest that will fit. I certainly cannot get the DA*50-135/2.8 in there. Well, not with a camera attached!
There's pockets on either side. My filters go in one side. Mostly the other side is left empty, but sometimes I throw in a DA40 in there or my Sony RX100 or a blower. The top lid has a small zippered pocket. I throw in an allen key for my tripod plates, the Pentax remote controller and a hotshoe spirit/bubble level in there. The front pocket is rather spacious, but well designed so nothing ever falls out. In there I've got my TriggerTrap cable, lens cloth, lens cleaning papers, Lens Pen, spare batteries and cards, a Sharpie pen, etc.
It's a fantastic camera bag and I absolutely love it with my Pentax kit. I am absolutely certain you cannot find a smaller bag to hold the K5 and 6 primes (incl the DA40 in a pocket). There's no wasted space, yet everything is easy to access and not "stuffed" in at all. The other great thing, is that when the camera is out of the bag, all the other lenses sit in the very bottom of the bag. This keeps the centre of gravity very low and the bag is well-balanced so it feels good on the shoulder and will never tip. I never close the clip (even though it's the best closure I've ever had on a bag) when the camera is out because everything in there is so secure and it makes accessing the contents of the bag even that much easier.
---------- Post added 10th Sep 2014 at 11:07 PM ----------
Hmm, my photos didn't seem to get inserted. It's been ages since I've inserted images into a posting here and I seem to have forgotten how. I can figure it out how, I'll try to fix it. In the meantime, if you right click on them and select Open Image in New Tab, it seems to work at my end. Hope it does for you too.