Still unsure which ZFS Configuration to use though

. I must say 2 x 4-way Raidz1 looks temping (with 1 Spare) since I can double IOPS compared to a single VDEV, yet more space-efficient than 4 x 2-Way Mirrors. 21TB usable vs 14TB usable basically ...
for me it would also depend on the use case - local storage - pump up the IOPS . Feed the beast.
network shared storage - I'd look at my max bandwidth, number of clients, and then the client use case. This method also presumes you have sufficient capacity for your needs regardless of how you construct the pool.
In my experience with typical and even a lot of synthetic but realistic (or trace-driven) workloads (not just bandwidth/iops testing) its hard to generate above 28-29Gbps.
There's an article floating around here (STH forums) somewhere that talks about the challenges of driving real world end-user and virt workloads above 40Gbps and trying to go even higher towards 100Gbps. <- I'm old I could be misremembering said article.
the only time I've gone above 35Gbps was a SAS2 12x2M of SSDs to another one doing a ZFS rep. Drive cap was 400Gb so not a lot of total capacity. it completed very very quickly. amusing first time. anti-climactic after that.