Hi Paul,
Many thanks for your reply. It's much appreciated and nice to see that intel employees show interest in customers' problems (makes a nice change sometimes)!
As I needed a working implementation within a certain timeframe I was left with little option but to reinstall using a different distro. My troubleshooting pretty much proved that the issue was related with some options set within the kernels packaged with proxmox. I am afraid I run out of time to troubleshoot this further at this point. At a guess if you had similar hardware at hand you shouldn't have much trouble reproducing the issue
Using the very same driver/module within a debian vanilla kernel (both stable and testing) works a treat. As a matter of fact I had multiqueue support out of the box with the debian kernel with an igb versions of 5.0.5-k (if memory serves) though I compiled the latest version of the module regardless.
I will however make notes of the above information for future reference.
Many thanks for your time,
Iakovos