You have quite a few problems with your PC, especially the extremely slow (by today's standards) USB 2.0 connection to any external devices. You see, USB 2.0 is severely limited in real-life sequential throughput to only around 40 MB/s in read speed and around 31 MB/s in write speed. That's far below what even the slowest HDD, let alone an SSD, can sustain.
And while that Xeon X5675 might have been powerful when it was new, it is a serious weakling by today's standards. In fact, it is actually weaker than a more recent quad-core 4th-Generation Intel I7-4790K CPU, let alone a current-generation 9th-Generation Intel i5-9400 CPU.
Put them both together, and you have a PC that gets completely choked with any type of multi-cam editing work.
And your GPU's performance is completely irrelevant, in this case, because the rest of your PC is a weakling.
The only fix for this, unfortunately, is an entirely new PC with much more up-to-date components.
Randall