Believe me, there are plenty of much slower compilers.
As for hardware vendors' compilers, it would be pretty embarrassing for them (not to mention pointless) if they _couldn't_ outperform competitors on their own hardware.
I'm also not so convinced by any "4% off gcc" claims about LLVM. Phoronix (yes, caveats aside) routinely test LLVM releases and it's common for LLVM to be a good 50% behind gcc. A lot of these claims you hear about LLVM's speed often turn out to be "when compared to a 3 year old gcc".
Not that I'm not an LLVM fan though. It's just important to be realistic.