While they are perched on top of each other, Fran, could you do a few direct A/B's of the same patches?
Please make sure that Mastering Tools presets are the same (if the E60 has Mastering tools, if not, defeat them on the G70).
I have heard a few things done on the Classic piano (supposedly the same as the GrandX patch in the G70), but it sounds MUCH darker, duller, whatever... Perhaps there is a cutoff tweak that could get it MUCH closer, but only someone with both would be able to compare. After that, it might be easier to see if Roland have compromised with shorter samples, or fewer.
Also, with the both of them sent to the same monitors, it might be possible to determine if the quality of the D/A's is the same, or has Roland cut corners a little (they tend to do this, like with the G1000/G600 comparison).
This is a fascinating opportunity to find out empirically what Roland do to make something SO close (in certain ways) to a G70 so affordable. Just be SURE you are doing apples to apples (make sure, for instance, that any Part EQ is defeated on both arrangers) and the volumes are identical (meters should be the same).
An arranger is just a tool. What matters is what you build with it..!