Run iozone to test pool.
Small tests will reside in ARC and give you false high. 512gb is minimum, or change tunable to reduce arc size
Iperf to test network.
FYI Scale has a bug limiting ARC to half your physical ram. Apparently there is beta test for fix posted on TrueNas forum. And should be in production in 6 months-ish. This won't impact synthetic tests, but in real life you may want to have the extra cache