Speedfusion vs Firmware versions?


Just a quick ask.

I have a few MAX 700 routers on the latest firmware, I also have a balance 380 HW5 on firmware 6.3.4.

I have used speedfusion between MAX 700 routers and after getting off to a rocky start I have learnt and they work fine now.
But now I am getting a much faster fibre internet connection into my office so thought I would add the 380 into the mix rather than LTE.

Whats the possible downside of running the MAX 700’s with LTE sims and a Balance 380 on Fibre with speedfusion? Will I be missing out on anything noticeable? Will it even work?