Not sure I understand what you are asking. You will probably never see the fastest speeds USB3 can provide since the version on the Quicksilver will be much slower. I'm sure you have heard of a "chain is no stronger than its weakest link". Same concept applies to most network systems; the speed of the network is only as fast as the slowest part
Nominal USB transfer rates:
- USB 2: 480 Mbps
- USB 3.1: 10 Gbps
Makes no difference if your drive is USB, Mechanical or SSD; it will never be faster than the network speed.
Perhaps when you upgrade the Mac, you can use the SSD on the USB speed you might have available then.
If the SSD can be returned, it might be possible to buy two Mechanical drives for the same price. You can then rotate those two drives on a weekly/monthly schedule.