One would guess that the middle seat will only be used when the load factor is higher than 80 %. But loads this high are very unusual in regional business. So I see a five-abreast plane to be more comfortable than a 4-abreast. And one has consider the "tube-effect". The ERJs are much thiner compared to the 728JEt or RJX-85/100. But only time will tell what is prefered by customers.