there isnt any type of ROUTER benchmark utility available.
there are many opensource routers/firewalls available, but you can benchmark one of their part, not WHOLE of them with any utility, as it doesnt makes sense.
e.g, By setting up PfSense firewall/router, you can add big RAM, good I/O controllers, high bandwidth/high throughput NIC and high speed processors and DISKS and then benchmark certain services like TCP throughput, DNS response time, squid proxy server benchmark, etc etc.
the biggest weakness of propriety routers is that they cannot be customized. but in case of opensource routers, you can add Tens of GBs of RAMs, Terabytes of Disks space for logs, and you can scale it to any possible way.
another issue with propriety routers is that the number of NIC available to them is limited, which is not an issue with opensource. as you are not bound to fixed hardware in them.
In my opinion, i would prefer PfSense, as i am using it on my network and using it to serve more than 10 services and about 8 different sites are connected through it. Everything is working perfectly fine without any type of delays or issues.