I trailride with the Kriega Hydro3 and the R8 waist pack. I'm 5'11 and around 200lbs without riding gear. I find this combo works pretty darn good even for aggressive trailriding. I won't lie, you can notice the R8 for sure, but I don't find it to be a problem at all. I run it at the back and it clears the Hydro3 well enough that there's no binding. When riding this setup doesn't impede me at all, but I do have to tighten the R8 up a few times a ride. Its by far the most comfy setup I've run in 10 years of riding. I've got a crappy zoomed in picture That I'll upload of the setup.
I really prefer having the R8 with my tools in it lower on my body. Having the tools plus 3L of water on my back seems a lot more draining when you get tired at the end of the day. Shifting the tool weight at waistline is a better setup for me.
Funny thing is, I'm also an insulin dependent Diabetic (since I was 4yo) and the R8 has that nice water/dust proof pouch in it for my glucometer & Insulin.. I've tested it a few times in water too.. held up great!
I'd recommend Kriega gear to anyone.