Hiya,
here's a *very* simple way to get a performance number for KDE:
$ time konsole -e sh -c exit
This gave me the following numbers:
0.75 seconds on a notebook, Sempron 3000+, SUSE 10.0
0.80 seconds on a desktop, Athlon XP+ 2000, Slackware 9.1, KDE compiled from svn
1.0 seconds on a notebook, Intel P4 M, 1.8 GHz, SUSE 10.0
1.0 seconds on a notebook, Intel P4 M, 1.8 GHz, kUbuntu 5.10