The main issue in populated areas is that there are too many routers sending WLAN signals, which leads to Wi-Fi interception, especially if you're using 2.4GHz signal(wider scope and more crowded than 5GHz).
Most routers auto-change the channel they are transmitting data through, and changing the channel manually isn't a solution.
The best remedy is to ...
USB3 is not going to be able to make up for a cheap and awful 2.5" HDD.
Those drives were pretty bad at the best of times and could probably manage 60-100MB/s at peak on a single solid transfer, for random seeks on small files they will literally drop down to single digit MB/s rates.
Have a look at the images for Seagate Backup drives at Anandtech. ...
This is probably not ideal and hopefully not the best solution, but you could create a VM using built-in Hyper-V (or whatever VM software you prefer) with the limits you prefer. That way, it is limited by the VM disk settings. I'll look around for other solutions when I get home and maybe we can find something.