Christian Vazquez and the Value of Pitch Framing » Last Word On Sports
They conclude that an elite framing catcher gets about 3 additional strike calls compared to an average catcher. Now a simple conversion 3 strikes = 1 out will be faulty for sure, but some of those calls will result in Ks, other will result in walks not given, and even if it just moves the count, that still affects batter performance. It does not however make a good pitcher bad, or a bad pitcher good.
And Russell Martin caught a knuckleballer in Toronto. His stats will obviously be miles different from non-knuckler starts then. He'll be happy catching the damn ball, never mind framing it, and umpires are not calling knucklers often and will probably call strikes and balls differently from a normal pitcher.