One more NIC on board = one more interrupt the CPU need to service. While the impact to the RT nature of Snakeoil shouldn't be impacted by much, it's still not an ideal setup. If you can, run the cyclic test (with music playing) with a single network vs 2 network and see if they are the same. Anything less than 10,000 will be fine (but the lower the better).
Might I interest you in a VLANed network with inter-VLAN routing?

![[Image: bled1.gif]](https://www.snakeoil-os.net/forums/images/onion/bled1.gif)
Problem is finding the right equipment - Ubiquiti/Unifi is over rated, HP isn't as good sounding, TP-Link is slow.