It looks the R920 is qualified only up to ESXi 6.5U3
The E7-4880 v2 is an Ivy Bridge CPU and therefore does not have the INVPCID instruction (comes with Haswell and newer). A modern OS with Meltdown patch without the INVPCID instruction that is I/O bound (network or disk or both) such as during an update after a fresh install of guest OS, will likely experience many VM-EXITs (VM handing control back to hypervisor and then back) and thus appear slow/sluggish.
10GB for VM virtual disk seems rather small. It is better to allocate a bit more to have free space within the VM virtual disk and best to have it as thick-provisioned.
The VM must be singing...
Ain't no particular driver I'm more compatible with, spending all these extra time without much....speed