i didn't upgrade mine right away and it was fine. i did do it later though and i think it feels much better. the clutch has a nice solid feel, plus you can have it grab where ever you like. so it isn't a must but i would.
i got a tune i just haven't update my sig. it's around 350 right now. it was extremly humid out that day though so i don't know for sure. it seems a little low to me but i am only seeing about 5-6 psi of boost. plus i asked for a very safe tune as i still have stock internals. now that the weather has cooled a little i might go back and get it redyno'ed. not sure yet.