@DKonkin, thanks for reading through our document of SpeedFusion Best Practices. If you have chance to review the page 6 of this document, you can find our recommendation below:
WAN links with different bandwidth profile (e.g. speed, latency, packet loss) may degrade the bonding performance.
Question 1
May I know what is the hardware revision of both Balance 710?
Question 2
May I know how you confirm the bandwidth above? Test with speedtest.net? If so, this is not an appropriate comparison with the SpeedFusion Bonding throughput. Have you noticed the nearest speed test server always be chosen when you do the speed test? Why? This is because throughput will be degraded (latency and packet loss will be increased as well) if the distance is further! This is well explained in the URL links below.
Question 3
Have you checked is there a bandwidth sharing between the WAN links? This is very common in broadband connection. This is well explained on page 10 of our document of SpeedFusion Best Practices. You might need to check with the ISP.
Since you have opened ticket, I would suggest follow up with our technical support there. Unless you wish get others opinion here.
Thanks.