I should probably confess to having not tried either of them! ;)
However it looks like support for the i217 was added in 8.4 and the i211 in 9.1. The branches confuse things there slightly since I think 9.1 was actually released before 8.4. Either way both are in 10.1.
Since the first inclusion I think things have changed slightly, I217 now appears to be in em:
@https://svnweb.freebsd.org/base/release/10.1.0/sys/dev/e1000/if_em.c?revision=274417&view=markup:
176 { 0x8086, E1000_DEV_ID_PCH_LPT_I217_LM, PCI_ANY_ID, PCI_ANY_ID, 0},
177 { 0x8086, E1000_DEV_ID_PCH_LPT_I217_V, PCI_ANY_ID, PCI_ANY_ID, 0},
And I211 in igb:
@https://svnweb.freebsd.org/base/release/10.1.0/sys/dev/e1000/if_igb.c?revision=274417&view=markup:
165 { 0x8086, E1000_DEV_ID_I211_COPPER, PCI_ANY_ID, PCI_ANY_ID, 0},
Steve