I remember a side by side of the S8+ with 4GB vs 6GB.
I guess really for double the storage & an extra 2GB of RAM for $60 more, it's almost a no brainer.
However, i'm just trying to get an idea from those of you who know more about RAM in phones than I do to chime in.
I'm also guessing it's normal to bump the RAM every time you bump the storage. At least I am starting to see that in some newer phones, (don't see a 128GB 5T with 6GB) but not all. You don't see the Pixels like that (and still with 4GB).
Seems to be RAM is all over the place & I always thought cost was the factor, but if OP can do 6GB & 8GB it doesn't appear to be that.