Newer drives are denser, so at the same rpm, they can transfer data faster.
Higher rpm mostly shows up as an important factor in random access vecause it reduces latency.
Cache/buffer size may be mostly marketing, drive vendors have built in the appropriate amount, and more is just a selling point.
If you want performance for the os, get a SSD. It is much faster than any conventional hard drive. Use a hard drive for storage and backups.