I know phoronix is not willing to test Gentoo due to its source-compiling philosophy. In this case, you may want to take a look at Funtoo, a variant of Gentoo (not a fork).

Funtoo has built for the following architectures already, so you really don't need to compile anything.

Stable Unstable Processor 32/64
amd64 ~amd64 Generic Intel or AMD 64-bit Processor 64-bit
phenom ~phenom AMD Phenom/Family 10 65nm Processors 64-bit
core2 ~core2 Intel Core 2 Series, i5, i7 or i9 Processor 64-bit
N/A ~core2_32 Intel Core 2 Series, i5, i7, i9 or Atom Processor 32-bit
opteron ~opteron AMD Athlon 64 or Opteron Processor 64-bit
N/A ~opteron_32 AMD Athlon 64 or Opteron Processor 32-bit
x86 ~x86 Generic x86 processor (intel 80486+) 32-bit
i686 ~i686 Generic P6-class (Pentium Pro/Pentium II compat.) 32-bit
N/A ~athlon-xp Athlon XP or Athlon 64-based CPU (32-bit mode) 32-bit

It would be appreciated if Phoronix could show us the performance comparison among these architecture stages on the same Intel/AMD CPUs.