I suppose most well educated people will get the biblical connection of the two names - personally I didn't though :) So I don't mind them as a sibset at all.
However I don't like
Ruth as a name, don't like the sound. While
Naomi is extremely feminine and soft,
Ruth just looks plain and boring next to it. imho.
Where I live
Naomi is always pronounced Nah-oh-mee - and I don't like the nay-oh-mee pronunciation either.