(in fact, because of the WAFL layout and NVRAM, writes might even be faster than reads. That of course assumes that your NVRAM is big enough)
___ Ya, more on that later if another reader doesn't do it sooner. I'm thumb typing right now.
NVRAM size has little to do with NetApp write performance. It is always big enough. More won't go faster. Less wont go slower.
NetApp writes to client are generally always fractions of a millisecond. Writes to disk user land never sees or feels directly.
Netapp does publish benchmarks for most of their storage systems, but these are usually based on benchmarks with LOTS of drives, so the netapp head itself is pushing its limits. With just a few dozen disks as the OP has, the netapp head won't be the limiting factor for any configuration.
___ You can never know that. No workload context exists here. It could easily be the bottleneck.