Could that be it? Under device manager I've unchecked the option of the computer to put the NIC in standby. I was under the assumption it wouldn't do any power management from that moment on. But you both seem very confident that would be the cause, also I've looked into this "selective USB suspend" and that's something I'll experiment with. Next time it goes slow, I'll unplug and replug the USB NIC.
+BudMan: http://www.neowin.ne...twork-transfer/ . My on-board NIC constantly produces CRC-errors during file transfers.
And yes, that's the current driver I'm using. I know it's a somewhat older laptop and it doesn't have USB3, still this USB NIC is a lot faster than my wireless card, especially during multiple down and uploads. Haven't checked my CPU usage though, will keep a Task Manager screen open on the background. Thanks for the tip!