Many thanks for your research.
1. Actually no I posted this post also: esxi and netapp MTU
Do you know if there's anything I can use to test the mtu settings with as I can't vmkping on an iscsi adapter?
2. The latest version of ontap we can use for our Netapps is 8.2.5 so we are going to upgrade from 8.2.3 but it looks like we won't be able to get the version that you have linked.