I had a chance to audition the Sennheiser IE-800 and I can't say it was significantly better than the GR07. Better? Yes, but my jaw did not hit the floor, not even close. It's getting harder to imagine that there is something good enough to make me want to get rid of it. I think maybe I'll get rid of my J3 before the GR07 - the DX50 is looking pretty dang sweet for $240 or so.
I'd say audition the ASG-2 if possible. We've both had similar journeys, and I think the ASG-2 is a good step up from the 07.
I'll possibly get my hands on another GR07 soon, so I'll PM you about the differences.