Re: CS27 vs C&C27
The CS 27 is well known for construction quality, and sails well, esp upwind.
The C&C 27 might be considered the 'prettier' boat, it's hard to beat the classic C&C sheerline, and personally I prefer C&C's hull deck joint treatment.
I think you'll find that cockpit-wise they are similar, the C&C may have a marginal edge in interior space and wider side decks for moving forward. Both have aluminum framed ports (C&C in earlier editions) that can be prone to leakage, but so can the bonded lenses on later C&Cs. IMO the newer bonded, tinted ports update the look of the C&C substantially.
The CS seems marginally powered if you have the original horizontal Yanmar, a friend has trouble powering much more than 4-4.5 knots, but there could be other issues at play there. Many C&Cs have A4s, which I don't believe CS ever did (but could be wrong about that) so that's another comparison point.
Don't think you could go wrong with a good example of either...
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)