The Romans did notice a physiological difference between themselves and Germanic Tribes, as already mentioned by DevSolar. The Arab traveller Ahmad ibn Fadlan aswell noted down in his journals when he encountered the Volga Vikings:
"I have never seen more perfect physical specimens, tall as date palms, blond and ruddy". Scandinavians still today ranks quite high on the average human height index.
Based on this i think it safe to say that there was some physiological difference between Vikings and other groups of people in Europe. But answering your question is hard because you group all other people living in Europe together as Europeans but dismiss and place the Norse in a separate distinct group. You miss to take into consideration that for example Germans have more in common with Norsemen but genetically and culturally than they have with Spaniards, yet you label both these groups together as Europeans.
Whether or not physiological differences have helped the Vikings in wars and conquests is hard to answer. It is logical that a bigger man has an advantage over a smaller man when it comes to combat, but in war there are so many different factors to consider. My personal opinion is that the possible advantage coming from physiological differences that might of occurred when the Vikings encountered and fought some of the other groups, is negligible.
There probably were some physiological differences, at least in height, between the Vikings and some of the other groups of people in Europe. But this difference is probably negligible and have not played any significant role in wars.