Your machine doesn't sound to bad for avchd footage. Resolve was only supporting Cuda (which is nvidia only I believe) up till R9 or 10 but they do have openCL support now so the ATI should be ok.
I think when you start CC'ing your footage in resolve you will see performance dropping quite a bit. Resolve uses your graphics card to encode for export, so it should be also faster than software encoding. I'm not sure how it will hold up against Edius though
One of the biggest issues I find though is that Resolve's workflow is all about having a good external grading monitor. You cannot trust the viewer in the resolve UI for color accuracy, especially if it's not a 10bit display with rec709 (or p3) colorspace. The learning curve for me in Resolve was steep, but I have to say it's also a very intuitive once you grasp the concepts and know the limitations.