New Build - need advice

System Specs (Old TrueNAS 12.0 “ish”):
Dell R540
Xeon Bronze 3106
16GB DDR4 2666 ECC
PERC H730P - HBA mode
Intel x520 /w 10 GB Fiber
Pool: 2 Pools of (6) 8TB 6G 7.2k Drives, each pool has a single Z2vdev
SMB shares

System Specs (New TrueNAS Core 13.0-U6.1 ):
Dell R750
Xeon Silver 4309Y
32GB DDR4 3200 ECC
PERC H755 - non-raid mode
Intel 350 (4)port 1GB NIC
Pool: 1 Pool consisting of 2 x (6) 8TB 6G 7.2k Drive Z2vdevs
SMB shares

Desktop (Win 10Pro):
Ryzen 7 5700
16 GB DDR4 3200
Samsung Pro 980 NVME SSD
Intel 1GB NIC

File copy results:
Old TrueNAS to New TrueNAS: mix of small and medium files - 17-19 MB/s, large files 69-87 MB/s
Old TrueNAS to Desktop: Same mix of backup files for small, medium and large files - 98-113 MB/s
*Results the same using Windows folder/folder copy, and TeraCopy

The large file copy from TrueNAS to TrueNAS is ok, but when copying a 70GB file to my desktop I saw immediate better preformance to the Samsung NVME.

This tutorial showed a R720 system with much worse processors, but much more RAM (200gb), and 12 10GB SAS drives. Sustaining 1.0 GB/s, they did tweak the blocksize to 1MB and used mirrors, but is that really the difference of 10x the speeds, or am I missing something else?

Looking for some help identifying:
Is there a calculator way to know what speeds I should expect on a pool setup?
Commands for verifying pool/disk speeds
Commands for verifying network speeds - I’m assuming network isnt the issue since the desktop was so much better, but considering LACP or a 10GB card in the new box.

I’m searching for some more RAM to beef up my ARC cache, but I think some of my downloading work flows and Tdarr services are really hammering my old NAS.

Would 2 Intel® Optane™ SSD P1600X drives mirrored as a 16GB slog be a good option for me?