Testing seems to indicate a 40% attack penalty on Resolution (Great Sword). That means you need 3.75x the mob's defense in order to cap cRatio. So, for example, you'd need about 1225 attack to cap cRatio against lvl 82 Greater Colibri (compared to something like Spinning Slash which would cap cRatio at about 490 att).

Of course then you need to run numbers to see how the overall weaponskill compares with its alternatives (number of hits, WSC, and the possibility of a drk being over attack cap on other weaponskills anyway). Still, it doesn't look pretty right now.