When I first installed Gentoo from a stage 3 (easiest) I downloaded the package cd also. It's possible to install a pre-compiled KDE in a few minutes using this - it defeats the object of using compile time options (USE flags) in this case and you won't always have the most up to date version of KDE but it's an extra option to consider.
For compiling KDE I'd also recomend you look at the USE flag
kdeenablefinal.
On a side note you can install a minimal version
Gnome with
Also, have a look at emerging ccache (check the online manual / forums) - enabling it should reduce the time it takes when you
recompile packages