Yes, well, that's a disappointment! i know the image scale of my 2.5x is bigger than with my 2x barlow, but I've never done a check to see by how much... (actually I haven't used the barlow much since getting the Powermate.)
I'd like to get a 4x Powermate for planetary imaging with the C8, but 4x is only available in 2". I'm not sure whether 5x would be able to be used too often unfortunately... f/50??? hmmm, have to be great seeing to use it!
Al.