Given that heroics and flash points (especially when done as your daily) are a GREAT boost to leveling, I love being Seer spec for one simply reason ... "Healer lfg - insert whatever" = insta invite almost everytime means you can get your daily's done that much quicker, means you can get back to questing that much faster.
Other then that, I have a TK sage mate in guild, and until my work load picked up recently, we were leveling at almost the same speed, using almost the same methods of daily space mission comobs, daily pvp reward, questing, daily flashpoints. So in the end I really dont think there is a noticeable difference.
Sure he can burn through mobs a bit faster, but he also wiped a lot more which offset his speed