My 2 cents:
a friend of mine got some Sensia 200 slide film. The first film was shot between spring and christmas 2010 and expired 10-2010. Then he stored the film until he got it developed at 06-2011.
Another roll (same expiry date) was shot in the winter of 2010-2011 and developed at the same time as the first film.
The first roll showed slightly more grain and a blueish color cast. The second one was pretty much perfect. They came from the same box of film.
The film was stored at room temperature (18-25 deg C)

When using slide film, i think it's best to develop within half a year after shooting and of course as soon as possible after the best before date.