Overall, Mac OS X 10.5.6 already outpaces Ubuntu 9.04 when it comes to many respects of the desktop and server performance. With the introduction of Mac OS X 10.6.0 "Snow Leopard" in a few months, the Apple gains will likely widen considering the efforts they are putting forth on improving the performance via a smaller memory footprint, OpenCL, etc. The graphics performance in Ubuntu 9.10, which will be out after the release of Mac OS X 10.6, may improve with Intel working to fix its regressions and Gallium3D could be enabled in time. Beyond improving the graphics performance and potentially some minor performance improvements thanks to an updated Linux kernel (well, a big improvement in SQLite unless they regress again) and the newer GCC 4.4 series, we would not anticipate the Ubuntu 9.10 performance to be drastically different.