It looks like LLVM/Clang mostly wins in SciMark, and these seem to be mostly matrix multiplications.
Sparse Matrix, Dense Matrix, Matrix Factorization, Jacobi *Matrix* Over-Relaxation.
Also there’s the Monte Carlo test, which might be implemented with Matrizes, too (I just wanted to check but could not find the sources).
So all these tests essentially evaluate the performance of matrix operations. And there I would ask: Which library?
When I installed scipy on our cluster (KIT HC3), it selected the best library among a number of libraries by actually compiling test code and doing runtime performance tests, because the libraries differ between platforms. Have a look at ATLAS ( http://math-atlas.sourceforge.net/ ) for some background.
The only other test where LLVM wins against GCC is Tachyon - and that likely uses matrix operations, too (because most 3D stuff can be represented by matrizes).
For all other tests LLVM loses. So the high number of Matrix tests skews the perception by placing a big focus on one feature.