Syinstall binary upgrade to FreeBSD 8.0

[David Jackson]

I would like to upgrade a 7.1 FreeBSD system to 8.0 FreeBSD using 
sysinstalls binary upgrade feature. I would mainly for now would like to 
upgrade the core OS and X and so on, but I still have some 7.1 binaries 
that will still be on the system. Is there binary compatability with 7.1 
binaries on 8.0. Binary compatability is pretty important to me. 
Anything else i need to know about? As for why I am not using 
freebsd-update, i did try it once it seemed as though it was going to 
take 7 hours to update the system., when the old way will have it done 
in 30 minutes. Thanks in advance.