From an Intel Core i7 4960X Ivy Bridge Extreme Edition system were these open-source server/workstation benchmarks being tested on clean installs of 12.04.4 LTS, 13.10, and 14.04 LTS. The stock settings and options were used.
To see these benchmark results, head on over to OpenBenchmarking.org. With Ubuntu 14.04 LTSs using the GCC 4.8 compiler compared to GCC 4.6 with the two-year-old Ubuntu 12.04 LTS, there's performance improvements in several of the different benchmarks used. To run your own benchmarks of the Ubuntu 14.04 Long Term Support release, it's incredibly easy to do so in a fully-automated manner using the open-source Phoronix Test Suite benchmarking software.