You state the router will be capable of 1Gbit WAN, but as a logtime user of OpenWRT I simply have to ask if this is 100% true.
Is the Turris Omnia router capable of handling 1Gbit NAT internet connection even with rules etc.?
On the OpenWRT user forum there are several discussions on slow performance on routers running with OpenWRT, which have HW-NAT capabilities running with their stock firmware.
And other routers based on the Marvell ARMADA 385 CPU like yours, have problems with OpenWRT and reaching 1Gbit NAT performance.
OpenWRT developers even claim that one would need a beefy x86 based router to handle 1Gbit WAN connection.