I have the Solo 3300 on the XCurve. Such an awesome bag. I picked up a used Serac 1700 in case I need a bigger bag. The Serac 1700 attaches nicely to the 3300. You also get the Serac to use as a day pack as well. Better option than the Access bag, imo.
I also have a solo bag with an x-curve frame, I love it. I ended up putting some belt pouches and a water bladder holder in mine which really made it even more awesome. It’s going to be perfect for my 3-4 day sheep and black tail hunts this coming up year. I’ve loaded it up with about 70lbs so far and it felt very comfortable. I really like the way the bag sort of detached from the frame so you can use the meat shelf, in my opinion that is an important feature and the reason I’ll likely buy a sky talus bag down the road and retire my kifaru to more backpacking/expedition use, that ability to keep the meat completely separate from the pack is a game changer for me.
As for the new Krux frame, I’m on the fence, it came out like 2 weeks after I got my x-curve and at first I was really bummed I didn’t wait for it and get the krux along with that 40/50 bag but in reality, I do have a large upper back from spending lots of time in the gym, doing pull-ups, push-ups, rowing etc and the x-curve fits well to the point that I’m just not sure a straight back frame would work all that well for me. I’ve never actually tried the krux frame but I’m just going to keep telling myself that so I don’t feel the need to get one.
Now that lightweight kifaru frame does have a curved back....that thing is tempting, I’m waiting to see what people think once they hit the real world.