Play what you like to play the most, thats all I'm gonna say.
not the way i see it otherwise id still be playing my necro :(
basically the way nc has made the olympiad the only class you should take to 80 is your main
Unless they make drastic changes in the Oly (and they may), the SH is as useless there at 75 as at 80, so you will need help from friends to make hero in any case and may as well leave him at 75. In contrast, an 80 necro will annihilate in pvp and sieges. Thus, in my view, the oly is irrelevant, and I'd level the necro on up.