Speed is relative to hardware.
On my intel laptop intel core duo t2600 2.16ghz + nvidia 7800gtx SL boots very fast as the bios is not first spamming it with bloatware ie 7.8 secs avg before loading modules.
On a crappy AMD box amd3800+ 64 bit with nvidia 7600gt card from hell it boots upto the modules loading in 16 secs.
This times is as it counts by itself after bloatware Asus / Dell bios loading.
Dell bios can take 3 to 4 secs, Asus takes 10 to 20+ secs depending on it's mood + sil sata and inbuilt sata nvidia raid programs loading during this time. Then only can it start.
Depedning on the settings and gdm or kdm and gnome or kde you are using you can be loged in under 30 secs or upto 1 min on both Ubuntu, SL and other linux.
SL for me on avg after fresh install and no tweaking gets to 30 to 40 secs on 4.1 gnome and with a few adjustments / killing the splash screen and rc.conf parallel "yes" this comes down a bit by 5 secs or more.
If you can kill the waisted time looking for a floppy in any linux during first 7 secs of which 4 secs is waisted on a non exsisting floppy drive search then it will be faster.
I have not seen floppy drives or floppy / stiffy disks available in most shops or used them in 8 years not sure if anyone else still uses them.
The other advantage SL based on Gentoo is it is easier than gentoo to get into and you can customize / rebuild it to be specific to your actual hardware / cpu amd or intel and get another 5 to 10 secs removed from boot times and in Ubuntu likely not , I think.
SL Install can take 30 mins to install or tweaked install at 15 mins on my laptop, same with desktop.
General after login speeds depending on drivers and config your out of the box SL should be faster and more responsive than Ubuntu and installing bin packages can take a bit more time than say Ubuntu.
You would have video / audio codecs by default and most things by default with normal install in SL and would have to add them using other linux distro's.
Hardware we do not have 20000+ guys / us$400m dedicated to only making SL work we only have 10 to 20 and user input + donations and with hardware again we have less to test only with user input and fixes / problems can we fix stuff.
Most reports from other switched users suggest we have better hardware support / it works out of the box or somethings does not / excotic hardware and can be made to work with a bit of user effort / easy enough to do. if you can read and follow a guide then it is fixed most of the times.
You would not feel so closterphobic / limited by the packages you find in other distro's as here if there is source code you can build it, where with say ubuntu the basic is easy and then you need to be a rocket scientist to get it working and then a nightmare from there on, their end game sucks. Here it is easy or med tought and stay's the same + a billion customizations / tweaking that you can do and not easily done with other distro's.
The question remains with you = the purporse + time / is this a hobby / toy , is it a working system that you rely on and how much time you are willing to explore linux with.
Do you need to install and only once in a while update ?
Will you be playing with virtualbox / vmware or similar to keep your system stable and test in virtualbox / vmware or chroot and build in the chroot area / jail type area ?
This is the questions that will make you decide as to Ubuntu or SL. Compare the live dvd from Ubuntu their latest and say a old copy of SL 3.5 or latest copy of SL and decide where your future lies.
Gentoo is not easy and you need balls and teeth of steel sometimes but only once in a while. if you can gentoo then all other distro's seems like easy toys to play and fix as 97% of the commands is the same except here you learn something.
How easy is it to completely break / destroy SL and then get it back to life / working perfectly, for me after completely raping my recent SL install it got it back to working in 3 hours and completely fixed withing 1.5 days not using anything else than a internet connection and what is installed. Yes even networkign was nuked and recovered.
If a baboon like me can do this with zero linux skill then anyone can do it by following advice and reading the wiki's / older forum posts etc / live chat top right of this page / on the desktop.
Hope this gives you a idea.http://www.sabayonlinux.org/screenshots