Well, My s8+ feels like the size of a iPhone 6+. And if you measure them they're about equal. More or less.
However, I was used to both iPhone 6+ and galaxy A7, which have the same screensize. So playing now with the s8+ 2 things come to my mind,
1 screensize is bigger but feels the same.
2 bodysize is bigger but feels the same.
I for one am glad I went for the s8+ since I too was debating this with myself. I'm not a pocket Phone person and I usually use the Phone with 2 hands.
So in short, the + size feels the same as any other 5,5" Phone, and the plain s8 will feel the same as 5,1 or 5,2"phones.
ps. screen width is smaller on standard s8, wider on the s8+ version. S8+ screen width is about the same as any other 5,5"screen.
So remember, it's taller but not wider.