The kernel part of the Linux drivers is written as soon as the developers get hardware from AMD. There are currently a half-dozen AMD employees working on this,

The kernel part of the Linux drivers is written as soon as the developers get hardware from AMD. There are currently a half-dozen AMD employees working on this, as well as a few non-AMD people, and generally, hardware support has been pretty concomitant with general releases of the hardware. "Slower" really depends on what you're doing. If you're doing lots of 2D stuff, then no, not by a long shot; the open drivers are generally very speedy for 2D stuff. If you're doing 3D stuff, then the raw framerates might be slower for games, but as a general rule, nobody's paid to make open drivers as fast as possible, only fast enough to run well. There's also a bit of disconnect between blessed AMD drivers and OEM drivers for Windows; there's known hardware which has never been supported by the AMD Windows drivers but works fine in Linux under the open driver stack. "Later" is kind of a loaded term; if you buy an AGP HD 2400 with a PCIe-to-AGP bridge, it has immediate Windows support, from the OEM, but with no updates and no upgrade path. Linux support lagged for that chipset by about four-six months but continues today, with updates and fixes. So, tl;dr: It varies so much that this question ends up being loaded.