Neville ChaimBerlin: “I’m not going any further with the baal gaavah argument. Clearly nobody in the real world holds that holding by Rabbeinu Tam’s tzeis or 16 amos reshus harabim is gaavah with the exception of a few CR posters.”
Baal gaavah argument? What? In any case, the argument regarding Rabbeinu Tam is if it was the accepted minhag. However, there is no doubt that shishim ribo was the accepted minhag, witness the eruvin in all shtetlach. Or as the Bais Ephraim argues, that all the Reshonim of Ashknaz accepted shishim ribo as a criterion.