Well, I'll chime in here. I have C-3 Limiteds, but I have spent many hours with the C-10 Limited. I have to say that if my small room could handle C-10 Limiteds, I'd love to have a pair. I think the coaxial arrangement is absolutely better than the separate drivers on the P series. I have heard C-10 Limiteds, and P-10's back to back in the same system, and there is a difference.
For me, there would not be enough difference to justify the cost. OTOH, if I had the cash, I would upgrade no doubt about it. I think the point about the bass being tighter and more healthy. The P-10 bass is amazing, but the C-10 is tighter. I think the C's have the advantage of not having that rearward firing tweeter. I think that's kew for ambience, but I don't think it actually helps the highs vs. the C series.
Good luck, and let us know what you do!