"Performance" includes two main metrics for disk access: Bandwidth and IOps.
The rotational speed of the platter disks affects IOps primarily. Faster disks => more IOps.
I have cheap older 5400 RPM disks in a home server than can pull 85MBps. A Seagate 300GB Cheetah 15K.7 (very modern disk) is specified at only 125MBps, not that much faster, but 10x the price.
But my drives get very poor IOps, like barely into the double digits. You need IOps if you're doing a lot of little reads/writes all over the place. The Cheetah drive gets 500 IOps (on average). So when writing a ton of tiny files or many small DB updates, the Cheetah will be about 50x faster.
Currently there are 5400, 7200, 10k, and 15k disks commonly available. Which you need depends on what you'll be doing with them. For archival storage, slow disks are cheap and still get good bandwidth. For OLTP you'd want the highest IOps money can buy. Most people fall somewhere in the middle.