I know 2 different women who have the Brooks Cascadias and the sales guy at the store I went to recently wears the Cascadias too. The women have had them for a while, and both said they love them. Neither woman runs as long as 6 miles usually, but that is more a reflection of who I can keep up with and chat to about their shoes than anything else, I think? I hesitated to post in case maybe you really should NOT stick with yours, so for what it's worth.
I was actually thinking about getting the Brooks Ghost last week, but then I liked the feel of the Nike Pegasus more. Those were the only 2 goretex trail shoes at the running store I was at, so that narrowed it down! I didn't buy either yet because there's a huge sale this Thursday, I'm planning to get one or the other then.
I hope your pain goes away now with these shoes or others!!!
EDITED TO ADD: I now regret buying the Nike Pegasus shoes. I wish I had gotten the Brooks Ghost. I have mild achilles tendonitis now (self diagnosed) and from what I have read, having squishier soles makes this more likely because your heel sinks into the sole farther. The Nike felt squishier and that's what I liked but now I know better. Hopefully you're pain free now (and hopefully nobody bought the Pegasus on my endorsement!)