Excellent! Changing the NICs in the VM to e1000 made all the difference.
I had considered this before but I couldn't change the existing NIC. Not knowing ESXi very well it took me a while to realize I had to add a new NIC in order to have the choice.
I've attached a new screenshot of the graphs during testing to compare for the curious.
Oh, and I'm not sure about the kernel not being SMP. In my system logs it says the following:
kernel: sullrich@FreeBSD_7.2_pfSense_1.2.3_snaps.pfsense.org:/usr/obj.pfSense/usr/pfSensesrc/src/sys/pfSense_SMP.7
pfsenseLowCPU.PNG
pfsenseLowCPU.PNG_thumb