In a post at the GuildWars2.com website, ArenaNet’s Bill Freist explains the ongoing optimization process and provides some performance data:
Guild Wars 2 engine programmers have made major client-side and back-end improvements over the past couple of months, including several different kinds of optimizations that have led to performance gains. Because we strive to ensure the smoothest player experience possible, we try to implement these changes only when they’ve been appropriately tested to ensure stability. This has led to the fluctuation in performance that many players have experienced through the Beta Weekend Events and stress tests.[. . .]
We’ve found other issues that can cause similar performance discrepancies. That said, even if it’s an external factor impacting performance, we’re going to work as hard as we can to ensure that your Guild Wars 2 experience isn’t hampered by poor performance. To that end, as issues are reported, investigated, and a fix is found, we will update our knowledge base. That way, the proper information will be made available to those that need it. The knowledge base will also include user-friendly instructions on how to fix performance problems.
There’s a chart of average framerate by GPU, showing how many of the supported video cards stack up against one another. (I notice that my Nvidia card doesn’t even show up in the table: more proof that I’ll need to replace it, I guess).