See my thread on it here: https://forums.macrumors.com/thread...et-up-to-1800-mb-sec-read-speeds-now.1922631/
But yes, generally a flash chip has higher read/write speeds the bigger its capacity.
A user likely wouldn't notice the performance difference from 64GB to 128GB. You may not even notice the difference from 16GB to 128GB without doing side by side comparisons.How much would this affect user experience? If anything, perhaps the difference from 16GB to 128GB would perhaps be noticeable, but would the difference between 64GB and 128GB be noticeable?