iWisdom wrote:phpBB3 is actually a little slower than phpBB2 (on smaller websites), but it performs and scales much better on larger websites.
i don't believe this is really the case.
i think a more accurate statement would be: "prosilver is slower than subsilver / subsilver2".
with phpbb2, as long as the site is small (and as long as you don't have MODs: many of the MODs are poorly written, with significant detrimental effect on performance), this advantage translates to faster loading, especially of the index page.
however, if you switch phpbb3 to subsilver2, my experience is that it is faster than phpbb2 for any size board.
of course, i might be wrong in this assessment, so the best thing to do, imo, if you encounter performance issues with phpbb3, would be to install/enable prosilver2, and try to see if the performance issue is present with the older template.
if subsilver2 does not demonstrate the same performance problem, it is still not clear-cut: personally, i think prosilver is worth the slight performance degradation price, but in any event, phpbb3 with subsilver2 is better then phpbb2 with subsilver in any possible respect, including performance.
just my 2c. if you find that i'm wrong here, please let us know.