That's a good argument for the figure, itself, but, once you factor in the sarcophagus, I think it becomes less compelling. The blues, reds. greens, and golds of the color edition bring out the detail much better than the grayscale scheme.
But, since your PF UM collection is comprised of SSE's you should probably keep the gray for continuity, and, as others have pointed out, it may be the more difficult piece the track down in the future.
If you do decide to sell the gray, I hope you will offer it to a fellow board member in the the spirit of the "Mummy Lottery Buddy Thread." I recall Jeff A. Simon and Vince were both left out in the cold.