Usually the president of the SBA is a 3L, so you have plenty of time for that. SBA basically doles out the money and runs some happy hours. I think that most lawyers realize that, so if you're looking for prestige, you're probably better off gunning for moot court or law journal. SBA people at our school are the gregarious. I think the speech thing really depends on the school- I think at my school all the speeches are given by those who have excelled in particular areas at the school, be it in academics, journal writing, oral advocacy or public interest. The SBA might have some role in commencement, but I'm not aware of it.