OEM will hold anything you're going to do with STi pinks.
An upgraded clutch will grip better, and slip less when you are shifting quick... but that will also shock your transmission more. I personally know someone who killed their 04 tranny with a 16g on pump gas less than a month after he upgraded his clutch. There's a reason people are recommending you stay with OEM. It may wear out sooner than a grippier clutch, but clutches are a lot cheaper to replace than transmissions.