Ubuntu 9.10 “Karmic Koala” will be out in October and does have some performance improvements as our earlier tests have shown, but Canonical engineers have not been exclusively focusing on performance optimizations with this release. Can the Karmic Koala outperform Snow Leopard? More here

Of the 26 tests shown in this article, Ubuntu 9.10 “Karmic Koala” was the clear winner in 12 of the 26 tests while Snow Leopard had won a handful and the rest of the tests had results that were too close to call or unchanged between the Apple and Canonical operating systems.