Why would you buy the Topeak Explorer rack if you are not going to use the Topeak quick-release panniers with it? Does the Axiom bag slide into the track of the Topeak Explorer?
I tortured myself shopping for panniers this past year and finally ended up with the Topeak MTX EXP or DXP (whichever is the larger one) trunk bag that converts into panniers. It's got plenty of room, slides on and off very easily, and has a shoulder strap.
As others might tell you, the zippers are not as high-quality as you'd expect them to be on such an expensive bag, but I've had no problems with them so far.