I actually just ordered a pair of Atrio M5s instead...I think the low end will be a bit better than the GR07s. Not to mention the fact that you can actually buy the Atrios right now. The GR07s are out of stock everywhere. If I'm not happy with the Atrios then I'll probably give the GR07s a shot.
I obviously haven't reach the diminishing returns threshold yet but I love having a piar of the 67s around for doing things that I wouldn't want to do in my 150 dollar earbuds (like yardwork). LOL.