Routing performance vastly depends on configuration. Each device has official benchmark results published as part of product page, hEX's are
here. The most optimistic reading says that hEX is capable of routing at almost 2Gbps (not via a single pair of 1Gbps lines obviously, tests are done using all ports at the same time and cumulative throughput is used as result).
However, most of users on this forum agree, that most indicative number for common real-life use cases is the one under "Routing - 25 filter rules - 512 byte [packets]", for hEX that's 385.4Mbps.
For a bit more complex setups even this number is optimistic. With lighter config, higher numbers are reachable. But until one configures quite a few routers, it's hard to predict how heavy will the setup be on device. So it's better to go with a conservative estimate.
Note that these tests are done only for IPv4 and fasttrack is heavily used. Fasttrack (so far) doesn't support IPv6, so results with IPv6 (which closely match IPv4 without fasttrack) are waay lower (my own hAP ac2 can do 1Gbps of IPv4 with sone CPU cycles to spare but struggles at less than 400Mbps with IPv6; official figure in the table I mentioned us at 980Mbps; config is mostly default).