Charles - I have experienced the same slow down as you, with both 24" and 44" paper (Satin Professional, in both cases).
I am using the latest firmware and drivers on a Windows XP SP2 box, and the only thing that makes any difference for me is that when printing landscape, it crawls as you describe, but when I flip the dimensions of the paper and then print the same image in portrait, it prints without interruption.
Good luck --
Ned Otter