Swampwalker,
I have never fired a cheek gonne, but I have fired shoulder stocked flinters and wheellocks, and I have fired many pistoles of various ignition. From this experience I would guess that there is no loss of accuracy. I believe that with the stock in contact with the cheek but not with the shoulder would actually serve to eliminate some of the tendency to waver the gonne while sighting and squeezing he trigger. Those old Germans of centuries past knew how to make and shoot firearms accurately. If cheek gonnes were so prevelant I believe they actually enhanced accuracy. However, this is just my opinion. Others will certainly think otherwise.
volatpluvia