First of all try to use fstab NFS mounts, as @fzinken has already said.
Since you’re on a Vero4K, you can go a bit wild on the caching and it still won’t “touch the sides”. I’d recommend you try 1 GB (
<memorysize>1073741824</memorysize>). A readfactor of 4 or 6 should be more than enough for high bitrate files.
The problem is that with a high bitrate file you’re going to be consuming most of the bandwidth just viewing the movie, giving you little spare bandwidth with which to build up the read-ahead cache. So it’s easy to recommend a large cache size but, in practice, you might never get anywhere close to filling it. And every time the bitrate exceeds the available network bandwidth, you’re going to start depleting the read-ahead cache - and with a high bitrate spike that depletion could be quite rapid.
If you want to see the caching in action, you need to attach a USB keyboard to your Vero4K and then reboot. Once Kodi has restarted, type Ctrl-Shift-o and take note of the “Forward:” figure at the top of the screen. That’s the amount of read-ahead cache you have accumulated. Then play a few high bitrate movies and see what happens.
Assuming that you’ve used the 1 GB cache size above, the maximum read-ahead buffer will be 75% of 512 GB, which is 384 GB. That will give a little over 30 seconds buffer at 100 Mbits/sec but only around 8 seconds at 400 Mbits/sec.