In a performance, I play naturally all the way up to D4 (use alt f key and octave key). I have ventured up as high as the G above that, however it is not always under control yet. Maybe by this time next year I will be able to do that. (alto)
On tenor, I play up to that G without a problem. It is a lower pitched horn and altissimo is easier to reach.
Peace,
Wolfram