Thanks--this is useful. So my OS drive stays on the SATA2 port.
And since latency will be lower on the SATA2, then that's preferable as well. I have no problems with latency now (knock on wood).
Latency in terms of drive access (the minimum amount of time a drive takes to respond to a request) is not the same as audio recording/playback latency, which is dependent on CPU and RAM. If you haven't had trouble with audio latency, good. If you
have had trouble with audio latency, faster storage probably won't help much. (Assuming you're not using some antique.)
But in terms of the Pro Tools project files that live on an HDD connected to the SATA, would those be better off on a small SSD? Would that make much of a difference? I use Pro Tools every day, so it is a priority.
I am finding conflicting information: some people say it changed their life, other people are lukewarm. So it probably depends on your individual case, workload, etc.
I think your best option (before you spend money!) is to use Resource Monitor (on Windows anyway) to watch your HDD access while you go through your audio workflow. If you ever hit a point where you're seeing >80 I/O per second, or you're seeing a burst of read/write activity at the same time you're
waiting for something to happen, that indicates you're (probably) bottlenecked by your HDD, and that's where an SSD will help you.
Maybe it's fine and you won't benefit from one. That would save you some bucks.