I love XenForo It's very modern, fast loading, user and mobile friendly.
However the rule of technology (universally), is it can only be as fast as it's slowest part.
For example, I can buy the newest i7 Intel CPU, pop in the latest motherboard, and load it with a server grade SSD drive, but if I go cheap on the ram that would be my bottleneck or the slowest part.
I hope I've explained the "slowest part" concept in away most people can understand it. But if not, please give your own example.
Software is no different and that includes forum software. No matter if you compare vBulletin, IPB, Burning Board, phpBB, SMF, or even XenForo there will be some point that you can say is the slowest part.
XenForo is fast and I love it.
But to me the slowest part appear to be deferred.php Even on XenForo.com running the file by its self is still 1/2 a second (between 200 - 500 ms)
Which of course calls upon
I've not really dugged to deep into the code & only have noticed how things load in Firebug. And of course 1/2 a second is nothing to cry about. XenForo should be proud that it's "slowest part" is only 1/2 a second compared to others.
Of course if you disagree with my opinion.... Where would you believe xenforo could be improved upon (where is it's slowest part)?