Presently, I have Gentoo installed on four partitions divided up like this:

/boot
/
/home
swap

The command du -h tells me this about the directories:

/bin 4.5 MB
/boot 100 MB # total space allocated, not du
/etc 4.3 MB
/home 4.7 GB # total space allocated, not du
/lib 13 MB
/opt 338 MB
/root 17 MB
/sbin 4.5 MB
/tmp 3 MB
/usr 2.1 GB
/var 771 MB

I have a new computer ordered which should be delivered within the week. I will do a fresh install of Gentoo on the new computer when it arrives.
I would like to make separate partitions for each of the directories like so:

/bin 20 MB
/boot 200 MB
/etc 20 MB
/home 9.7 GB
/lib 30 MB
/opt 1 GB
/root 30 MB
/sbin 20 MB
/tmp 2 GB
/usr 6 GB
/var 1 GB

The present sytem does not have KDE or GNOME installed and has the OpenOffice 1.1 Beta binaries in /opt, with all binaries stripped. The new system will have KDE and GNOME installed. Once OpenOffice 1.1 Beta is final and has an ebuild, I most likely will emerge it. I want to make
sure there is enough space in /tmp to emerge OpenOffice down the road and also make sure there is enough space in /usr to accomodate KDE & GNOME.

Will this partitioning scheme work or are there any directories that should be adjusted as far as allocated space? Additionally, what would be the best way to order the partitions on the disk,to have maximum responsiveness on this system?

Any help or ideas are appreciated.