So, I'm trying to draw Mr. Denny Conn out here. Have you noticed any thing different (off flavors, etc...) just pitching the dry yeast pack without rehydrating? Anything over 1.060 I just pitch two packs, but is the rumor true that if you pitch dry yeast, without rehydrating, it kills half the cells instantly? This doesn't really make any sense to me, as I usually rehydrate in around 85 degree water. Wouldn't that kill some cells too? Why does it make a difference when you pitch into wort, is it because of the sugar content, like it's such a shock to the yeast? Just need a little food for thought.
My experience has been that straight into the carboy is fine with lower gravity worts and one packet. If the OG warrants anything more than that, pitching two packets dried consistently gives me off flavors so I don't do it anymore.
I rehydrate. Always.
No off flavors ever, save for my recent experience with adding go-ferm to the rehydration water which I do not recommend.
Pitching dry straight into the wort forces the yeast cells to rehydrate with wort, which has hops compounds and substances that invade the cell and kill it. Many more cells die than by using straight water. My theory is pitching two packets adds more dead cells which are what contribute to the off flavors, not to mention any resulting underpitch as a result, which also adds off flavors.
Warm water is better for them. Follow the recommendations from the yeast manufacturer and I think you'll be happiest with results.