Slow SSD speeds on internal SATA (MBP 8,1)

Howdy, all!

I have a MacBook Pro 8,1 (Early 2011) with an aftermarket SATA SSD that I installed. It's running the latest OCLP and Ventura versions as of this post. One thing I've noticed no matter what OS I run on it is slow disk speed.

The speeds I get are roughly 120MB/s (read/write are nearly identical) when tested with Blackmagic. Chunk size in Blackmagic doesn't have a meaningful effect, so I don't feel like it's the app.

I know common issues like the SATA cable (they're so fragile) and my SSD could be the culprit.

Is this a known issue that slipped my mind, and/or do any of you running the same model experience similar disk speed issues?

Author: @Unwiredsoul