Bigfrank83 wrote:
1. Run ESXi from a USB stick
2. Use Add-in NIC for Management (This NIC will also supply network connectivity to your 2 Gentoo VM's as you will have passed through the other ports to an individual VM)
3. Pass through on-board Dual NIC to pfSense VM
4. Use RDM for HDD's. After all, you're gona need a datastore for the VM's and if you pass through the controller to a single VM, you have no ports for your datastore.
Sorry for the delay; done some background reading.
1. Why a USB stick? If I do could I use a lockable stick? (assuming no config changes)
2. I intend to just use a virtual switch for my two Gentoo installs - the passed through devices will be for pfsense. Will the combination between a virtual NIC and RDM be too much for the CPU on my NAS? (one of the Gentoo installs) I am attempting to write at gigabit speeds from time to time - mainly for backups.
4. I read up a little on RDM - Is there a performance hit when using it; does it utilise a lot of CPU? I assume the 'Raw' in RDM means I have raw access to the disk and hence I can format any file system - but does the data reside inside any container.. or is it 'raw' on disk? Silly question really. 
I don't want system snapshots hosing any data.
Q: I noticed that PCI passthrough requires an ACS capable PCI switch - this has been included since the PCI 2.0 specification right? So it shouldn't be a problem?
"BTW, jellyfish, I have a DQ77MK at home, although it's running Debian 7, not ESXi 
. Let me know if I can collect any info to help with your purchasing decision..."
Yeah that would be helpful:
1) The BIOS - does it support Enhanced SpeedStep? i.e. frequency scaling. There is suppose to be a section in the CMOS on supported board.
2) Is there an option for enabling VT-d in the CMOS? Some affirmative confirmation for this would be great.
3) Do you run KVM at all? It supports VT-d - if it's not too much out of your way perhaps you could try it out... but perhaps that's asking too much. 
Thanks for the helpful replies guys.