LTE Cat.6 feat. Pepwave HD4 MAX

Hi, everybody! I have pepwave HD4 MAX router (Hardware Revision - 3, Product code - MAX-HD4-LTE-E) and use all 4 Cellulars (LTE cat.4) as uplink. Now I want to replace Cat.4 modems with Cat.6 modems.
At the moment I am testing a combination of 1+3 (one Cat.6 and three Cat.4) and I don’t see any problems
But what happens if i use, for example, a combination of 2+2 (two Cat.4+two Cat.6), or Full 4 (4x Cat.6)?
Will there be serious problems with CPU utilization and device temperature rise? Which combination of Cat.6 and Cat.4 modems can I use safely and efficiently on HD 4 MAX?
What other problems can there be?