I owned the GR8 a long time ago and can't really speak of the difference in any truly accurate capacity. Off memory though, I do remember that the GR8 is a bit less refined across the board. I think the GR10's highs are less grainy and the bass is a bit tighter. I think the GR8 was a bit warmer. Again, this is all from memory and not a proper a/b test. I would suspect that if you were to buy the GR8 and never listen to the GR10, you would be a happy camper. I was once told that if Etymotic made the GR8 and GR10, the GR8 would be the warmer version of the ER-4 and the GR10 would be the next evolutionary step up. From my experience with Grado and Etymotic, I can agree with this assessment.
But please, I am not a Grado fan boy, and can see why you'd go with the Etymotic (cost being one reason--though the GR8 used can go for around $175-200); but I do still stand by my statement that you need to match them right or they'll sound too thin. I agree with people who say that the Comply tips work well with Etymotics. I personally really liked the longer P-Series tips, as they helped warm-up the sound and were a little more comfortable.
What about the Westone 2? It doesn't get a lot of love around here, but I've heard that it's pretty impressive for its price.