Efficient for me means best buck for best performance&features/watt.
If this means the same to you, get the Mikrotik.
For just routing and NAT, an i3 can handle 10 Gbps with lots of room to spare. An i9 9900k is just for show and to heat the room during winter.
we are using the CCR1072 and the CCR1036 (the last one is available with two SFP+ interfaces) as Firewall and for NAT. If you need more than two SFP+ interfaces, take the 1072, if you are fine with two, think about the CCR1036.
The performance in our case is more than enough even if we push ~6-7GBit through the firewall, the CCR is just idling. We are using statefull firewall rules + FastPath/FastTrack so a lot of computation is done in hardware. If you have a lot of IPv6 traffic the CPU load will be higher, because FastPath/FastTrack works a the moment only with IPv4 traffic.
I let iperf run between different subnets, so the CCR1072 is doing firewall and routing: >9GBit For our needs the CCR1072 is perfect, fast and also a low power consumption. Can you specify how many traffic you expect and which protocol you are planning to use (udp/tcp)?