RockPro64 iperf3 ure vs awge results

[joelp%sdf.org@localhost]

Hello -- I plugged in a USB C network adapter as a test in case I need to
use my NetBSD 10.0_BETA (ROCKPRO64) #0: Sat Sep 23 13:31:09 PDT 2023 build
for a RockPro64 as a router in a pinch; dmesg:
ure0: Belkin (0x0bda) Belkin USB-C LAN (0x8153), rev 3.00/30.00, addr 1

Generally, it's looking good, and the USB C adapter has been stable during
testing with iperf3. One thing I noticed though:
- awge0 (built-in) interface result is ~350 Mbits/sec.
- ure0 interface result is almost twice at ~660 MBits/sec.

I tried various changes on my network switch with VLANs, different server,
IPv4 vs IPv6, and results are roughly the same: I just can't see anything
locally on my LAN that would contribute to such a bandwidth diff between
NICs.

Is it expected on a RockPro64 that the built-in NIC is slower than a USB C
NIC?

Thanks - Joel