Ubuntu 14.04 vs. Debian 7.3 vs. Debian Jessie Preview
The newer kernel also helps out Debian Jessie compete in some benchmarks. Jessie is also using the Intel P-State driver on Linux 3.12 for this Ivy Bridge low-power system from CompuLab.
While there are compiler and kernel differences, for some system benchmarks there is little impact by changing out the used Linux distribution.
Debian leads over Ubuntu 14.04 LTS in some of the benchmarks.