upgrading dhcpd from 3.0.5 to 3.1.x

[Joe in MPLS]

I am running a failover pair of dhcp servers. One server is FreeBSD 6.3 
STABLE with dhcpd V3.0.5RC2, and the other is FreeBSD 7.0-STABLE running 
dhcpd V3.0.5.

I want to upgrade these servers to dhcpd V3.1.1.1 (the latest in the 
FreeBSD ports collection). How do I determine if my existing config 
files and lease files are fully compatible with the new version? README 
and RELNOTES are silent on this.

"RELNOTES" says the failover mechanism is "significantly enhanced". Is 
it compatible with the older version? I'd like to avoid the risk 
involved in upgrading both servers simultaneously.

             TIA   ...jgm