SELECT-only test
When running the simple read-only test, results will be very good while the database fits in RAM, then dropping off fast after that. Note that the straight line you'll see on all these graphs is always the database size value, which is in units shown by the right axis scale.
This curve has a similar shape no matter what hardware you have. The only thing that changes is where the two big break points are at, depending on how much RAM is in the server. You're limited by the speed of well cached system RAM on the left side, by disk seek rate on the right, and some mix of the two in between.