Well, then it's true, it's better if you find a way to use FreeType directly. I don't know how to do it, though.
I have never heard this particular problem with spaces, but indeed Allegro has some problems when drawing fonts.
There is a way to cache the text you want to draw before drawing it, that should make everything faster but it's a hacky (not elegant) way of doing it.
It's a real hack: you just have to draw the text before using it... Yep take the drawing function and draw all the characters and numbers of your alphabet, after that, it should be faster...
Instead of drawing, you can also use the al_get_text_width() function. Do something like this:
That should improve a bit.
But If you're having problems with spaces... I really don't know...
Now, I know this may sound a little bit crazy, but at the same time if you're experiencing too much lag when drawing fonts using Allegro, it's because you're using text a lot, so for that reason it might be better to use SFML since it handles better the font drawing operations.
Because I don't know, using FreeType directly doesn't sound like a good idea to me.
Have you created the font before or after creating the display?