Hello JJ,
SSG140 in my lab can support 2048 routes.
max multicast policy num per unit number: 50
max Multicast routing table owners number: 16
max output interfaces in multicast route number: 2 <------- Appears to be related to load balancing.
max multicast routes number: 2048 <--------- These are number of routes.
SRX is much more scalable when it comes to routing & SRX550's capacity would be at least 3-4 times (perhaps even more) more than SSG140.
Regards,
Rushi