My take on SL is that it was just a way to get Fermilab and CERN to standardize their platform. By the way saikee, this
is the SL I'm looking at, from your description you may be looking at something else. Or am I wrong? The reason I'm asking is that the one I'm looking at seems to be RHEL based, not Knoppix, and the state that they don't include any scientific software.
At any rate, I think the deciding factor here ought to be your needs. Personally, I don't see anything in SL that makes it a real standout from other distros. And I don't know if there is enough of a performance issue from distro to distro to help much. My experience is that performance is more dependant on the tweaking of the install than the actual distro.