I have made some measurements. Downloading large files through Tor did not appear to show significant differences between both nodes, which could mean that Tor clients are either capped in general or the circuits were overall not fast enough to make my nodes reach their limits.
I also tried several iperf3 bandwidth measurements between the two Tor nodes and a third server which I know to be reliably fast. My Tor node #1 averaged 697 Mbits/sec, and #2 averaged 505 Mbits/sec -- while Tor was running on both nodes. I tried this with both IPv4 and IPv6, the latter being slightly faster.
It would appear that even though #2 has less bandwidth than #1, the available bandwidth of #2 is more than 10 times the bandwidth utilized by Tor on this machine. I still don't understand why TorRelay02HORUS is just limping along.
-Ralph