I hope you've seen European Oak. Widely available. The grain isn't as open as NA white and red oak. This means flat cut that can better show the patterns of the wood work well aesthetically. This property exploits the stable construction possible with engineered planks. 7" or more would be my choice if I liked looking at the patterns of wood. Even if the rooms were smaller. Pick a width that shows the beauty of the wood. Monarch Plank has examples.

Thanks dan1888. I have considered European Oak. I forgot to mention that I am doing a rift and quarter cut.

The NA oak open grain problem is more acceptable when rift and quartersawn is the pattern for quercus alba, white oak. European oak is a different species, quercus robur. Denser with less open grain and less yellow cast. Bona has a product Red Out to treat red oak to get the tone closer to white oak or European oak if the grain is filled with a pale color. If you use rift cut the width doesn't show the flat cut pattern. Width isn't as important. Wider will only signify higher quality.

Usually I think bigger objects make a small space feel bigger. However, in this case, I would do 4 3/8".

Thanks Kendrah. May I ask why you recommend going smaller in this case?

What dimensions are you working with?

IMO you will not see any big difference with 1/8 " change and I think with european oak I would do the wide boards

With finely matched floors like oak don’t overthink the board width. It just isn’t as dominant a design element as it seems right now. A busier floor like a camp grade oak or something with light and dark areas the board width is much more important.