The delay may have something to do with the fact that the OpenGL level was upgraded to 4.1 with Mavericks, so they also have to implement new OpenGL functionality into all the drivers. For instance, now the drivers need to support tessellation, among other things.
And it seems they're not exactly up to the par of Windows 8.1, and from the comments on that post, it seems those are beaten even more so by running the benchmark from Linux. How much of this is up to the display drivers, and how much is up to the operating system API layers, is unknown to me, but maybe somebody knows.
I do know that I was recently attempting to play Legend of Zelda: Twilight Princess in Dolphin 4.0, and the new GLSL code makes it slow down to 80% or worse solely due to the GPU. And it regularly causes the GPU to lock up, which halts everything on the display including other applications on my second monitor, except for the mouse cursor.
I would play it on my Wii, since I bought it years ago, but I hate the waggle controls. Hence the GameCube version in an emulator.
Off topic, but vaguely related. Maybe updated web drivers could make that playable, or maybe not. In the mean time, I'll stick to playing it in my dual boot Linux setup.