My goal is, even if BTC Guild shrinks as more and more massive private farms come online taking a larger chunk of the mining pie, to keep our shift N value at least 10% higher than network difficulty.  This provides a total 'N' value of 11x difficulty, which is a length I don't believe BTC Guild has ever seen a block take (I think it has only happened once out of any pool in the last 3 years).  Obviously there is always a balance of maturation time for shares vs variance