I think the Mctavish is dressier than the neumok, because of the distressed look of the neumok. That being said I wear my neumoks on casual days with courds. I love my neumoks and would have gotten some cognac mctavish, but the mctavish fits much different than the other 5 lasted shoes I have.
You should get the McTavish anyway - yes, completely agree it is different. Some of the 65s fit larger than the others, like the McTavish, Black Hills etc. but I can usually get by with heavier socks. As much as I love the Neumok, I wear the McTavish way more often. Not to mention with the Neumok being unlined, I freeze my @$$ off with it wearing it in the winter weather.