Funny this was brought up.. processed a roll of Fuji Fortia SP for someone a few days ago.. it must have been stored perfectly, as it was like new. Looked fairly normal (no funky tones or colour casts) just with really intense colour on a light table.
I used to take my E-6 films to Horiuchi Color (a nation-wide pro lab) when I was in Japan. They said if stored properly it could last a while, and indeed people were still bringing it in on occasion. That was maybe 2 years ago. I keep mine in the freezer.