Hi!
Routing performance wise MAX Orbit 2 and MAX Orbit 4 are similar to the BR1 Pro 5G and BR2 Pro 5G.
The difference is in the LAN and WAN ports.
For example the BR2 pro 5G has 2.5Gbps WAN ports and 1Gbps LAN ports. The Orbit 4 has 1Gbps WAN ports and 2.5Gbps LAN ports. Please know that the 2.5Gbps ports are swappable into WAN ports. Usefull if you want to play around with this 
The MAX Orbit 8 is similar to the just released Balance 310 5G in performance. Again the LAN and WAN ports are different in configuration.
Release page for the Balance 310 5G: Balance 310 5G - Reliable Enterprise Branch Networks. Simplified
Hope this helps. 