I've captained several Grand Banks and recently moved an Offshore 54. My friend owns a Grand Banks HX and while it is a great boat, it is not comparable to an Offshore. Both fruits, but apples and oranges.
The Offshore is much more of a long distance boat, designed to handle unexpected weather and changing sea state (hull design, stabilizers, etc.). I'd say the Offshore is like a Nordhavn, without some of the redundant bits, and it can travel faster (but that will cost you in fuel). We burnt 3 GPH cruising at ~7 knots over 2 days non-stop. It was a 2001 with the big engines. I was surprised how economical the boat was at lower speeds.
The GB is more of a coastal cruiser. The Eastbay is great, but very tight spaces, which makes it harder to work on. Tight spaces relate to work taking longer, and if you don't do the work yourself, that means more money spent on labor.
It's completely different type of boat. One is built for extended trips, the other is a great weekend cruiser.