Inara Prey recently wrote an article on Comparative Viewer Frame Rate performance. It is a handy reference. It took lots of effort to collect those numbers, which is why I seldom do rigorous tests.
Somewhat surprisingly it is the Linden Lab’s 3.2.5 viewer that is the fastest in the comparisons. I use the Development viewer 3.2.6, which is a little faster for me than 3.2.5.
The Lab’s viewers have not updated over the holidays. We may see some updates today or tomorrow. I suspect the Lindens are just getting back from the holidays and getting back into things. Also, it is a new year. People are fresh from a break and we may see some things change as they look at things with fresh eyes. Time will tell.
The main viewer is now 3.2.4. The beta version is 3.2.5. And the development viewer is 3.2.6.
The 3.2.6 is said to be the release with most of the Shining branch’s OpenGL fixes and changes for compatibility. I’ve been using a 3.2.6 version since December 12th (246465) with four updates; 246560, 246813, 246889, and now 246959. Of that series the 246959 version is the fastest, but not by much on my system.

