I am in a similar situation but with a 60D + 100-400 being carted around Acadia. I LOVE my Domke strap which I've owned for nearly 30 years, but this trip has shown that it is not good for this kind of weight and movement.
I have looked at the Carry Speed, Black Rapid, and Joby. Not sure which I'll go with though it looks like the CS and Joby can be used on and off tripod seamlessly, but not the BR. That said, I have also found in my experience that dual-purpose can often mean dual-compromise as well.
Any thoughts are welcome. Other than eventually moving to either a 6D, 5D3, or other larger camera, I have no allegiances to any of the strap systems.