Choose a Larger SSD for Faster Speed
If you’re weighing your option between SSDs and can’t justify buying a larger version, it can be confusing: Larger SSDs generally run faster as well.
As How-To Geek explains, SSDs operate using NAND chips, not spinning platters of hard drives. To increase the capacity of an SSD, manufacturers have to add more chips. When they do this, they usually arrange these ICs so that they can be used in parallel. In other words, a larger SSD can write, say, eight NAND chips at the same time, rather than four as a smaller SSD would.
This provides a speed advantage for larger SSDs in terms of bandwidth. While your mileage will obviously depend on how the manufacturer built the SSD and how big the difference in capacity you’re looking at is, overall, the smaller the SSD, the slower you can expect it to be. It will still be faster than most conventional hard drives though.
Why are smaller SSDs slower? | How-To Geek