Well I think that altissimo is one of the fun parts about the saxophone. The bueaty of the instrument is that it is very versitle and its cool to explore that. If you dont take the time to learn a little altissimo you'll miss out on a lot of important literature, such as Introduction and Samba by Whitney, the Ibert Concerto Da Camera, and the Muczynski Sonata. Generally an octave above F is all the practical altissimo you should need. I really only go up to high D, the higher you go the harder it is to control the sound. As far as learning through books I think the Rasher and Rousseau methods are great for altissimo voicing but honestly I just look for the right fingerings and check the note with a tuner to know the correct pitch. That's my little bit.