Scaling up on more hardware is always an option, but I really want to push the limit of the exit node, as the others won't be exits (Local network design, really) , and exit traffic is always more interesting.
When I say another instance, it’s on the same hardware. Because Tor is not fully multi-thread/multi-core, you have to run another Tor daemon on the same host to use 1 more CPU core and so drain another 150-300Mbps. Currenly, you can start up to 2 Tor daemons per IP, there is a limitation to avoid Sybil attack.
Regards,