If you want to rule out most everything software, you can use dd and nc to benchmark file transfers with minimal overhead. iperf also your friend of course :)

Does the raspberry pi have a wifi adapter, and is it unused for your project?

If so, you can use your pi as an access point — no need for cables, you just connect your laptop to the pi’s SSID.

Downside is that now your laptop doesn’t have Internet access, which may be a deal breaker (unless you can plug your pi into a router and get access through it). You could just get a cheap USB wifi dongle for your laptop and use one interface for Internet, one for pi.

Hostapd is probably how you would go about this of you’re interested ( https://learn.adafruit.com/setting-up-a-raspberry-pi-as-a-wifi-access-point/install-software )