Hello,
Thank you for reaching out! Unfortunately, RUTX14 is only designed to work with one SIM at a time, and the second SIM is meant for failover. For load balancing between two SIMs, you'd need RUTX12, which has two Cat 6 LTE modems.
However, if bandwidth is the main priority, RUTX14 contains Cat 12 modem, for which the maximum theoretical downlink speed is 600Mbps. RUTX12 contains two Cat 6 modems, with 300Mbps maximum theoretical downlink for each modem. So theoretically, if your carrier supports Cat 12, you should be able to get similar speeds as using two Cat 6 modems.
Another advantage would be that RUTX14 would allow a single link to utilize the entire bandwidth. Load balancing, on the other hand, is designed to aid in balancing the load across multiple links.
Let me know if there is anything else I can help with.
Best regards,
DaumantasG