Say you wanted to create a new PHP forum that was very flexible in it's UI design. More flexible than Xenforo, for example. Is there a danger all this flexibility can slow things down ? or does the flexibility come free (no cost) ? Would it be just dreaming to say you could make a more flexible forum that doesn't sacrifice speed ? or is the sacrifice in the difficulty ($$$) to customize an already custom UI ? Would it be super hard to support a forum software package that was super flexible (ie. every site is different) ? Thoughts ?