The focal length of a scope is determined by the diameter of the mirror, divided by the distance it takes the image to come into focus. So a 6 inch F8 mirror comes into focus at 48 inches. Your C8 is shorter because it has a folded light path, but you'll be able to have a good idea of the f.l. The most significant difference between the differing focal lengths is that longer focal lengths give a larger magnification with an identical focal length eyepiece, and shorter focal length mirrors suffer more from coma, the coma becoming increasingly worse as the f.l. goes down. Portability can also be a factor.
Laminated glass can be a real problem.
Unless you absolutely can't get get a blank any other way, I wouldn't do it. An 11 or 12 inch mirror wouldn't be too bad with this thickness of glass. Hope this helps.