As Val said some features in later releases will require USFW so switching back to kernel mode will become less and less relevant, even on smaller boxes. Your 6200 has only two physical CPUs with SMT enabled for 4 total cores/threads.
Your 6200 seems to be handling the load fine and there are no tuning adjustments required, plenty of headroom. I suspect the higher CPU load on your 6200 is due to the CPU number and/or type differences between it and your prior open hardware. What was the prior open hardware model and CPU type? If it was some kind of Xeon which is common on Intel-based servers, that Xeon CPU is probably at least twice as fast per-core than the Pentium Gold G5400 in your 6200. As long as a firewall's cores are not normally running north of 75% and topping out at 100% during the busiest periods you should be fine.
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