There are three things that affect the performance of a modern disk drive.
For the first two, you kinda have to know how a hard drive works. The OP probably understands most of this already, but for the benefit of others reading this thread I’ll explain it. The disk drive has disks in it which spin. Over top of the disk you have a “head” which reads from or writes to the disk. The data is arranged like rings on a tree. To access the data, the drive first has to move the head over the correct “ring”. Then the head can read or write the data as the disk platter spins underneath it.
So, the first two things that affect performance is (1) how quickly you can get the head into position, and (2) how fast the platter spins under the head. The first one is called the track to track seek time. This is a time measurement, so the lower the number the better. The second is the RPM of the drive. Faster (higher RPM number) is better.
Back in the old days, that’s all you really needed to know, but modern drives cache data. If you read track 7 sector 1, then track 7 sector 2, then track 7 sector 3, it’s a good bet that track 7 sector 4 is coming next. Modern disk drives are smart enough to know this, and recognize certain other patterns as well, so what they do is they go ahead and read in track 7 sector 4 before you even bother to ask for it. This way the data is already in the drive’s cache memory when the computer comes along and asks for it, and then the computer doesn’t have to wait for the drive head to move and the data to be read from the platter. Generally speaking, the more caching you do, the better performance you’ll get, though this is only generally speaking. The caching algorithms used also come into play, but drive manufacturers don’t tend to publish much about that. Basically, as you are looking at specs, the more cache the better.