Phoronix published a review on the Ubuntu 14.04 vs. Debian 7.3 vs. Debian Jessie Preview
A quote from the article:
For those curious about performance differences between the current Debian 7.3 "Wheezy" stable release and the upcoming but currently unstable Debian 8.0 "Jessie", here are some performance benchmarks comparing Debian's stable and testing releases on the same hardware. Making things more interesting, Ubuntu 14.04 LTS in its current development form was also tossed into the mix.Ubuntu 14.04 vs. Debian 7.3 vs. Debian Jessie Preview @ Phoronix