I have a Greystone 32re and love it . Greystones and Sundances are built by the same people on the same line at Heartland, and share the same brand manager. They share the same frame and axle components.
The Greystone differences that I know of are:
1) outside siding on the Greystones are different and much better, we get lots of complements.
2) cabinets are two tone, we find this makes it brighter inside
3) flooring is nicer in the Greystone
4) counter tops are solid material, like corion
I look at the Greystone as the deluxe version of the well made Sundance unit.