Replying to "Fat" Skis? = Slow?

So hey all, I just got a pair of 2010 K2 Extremes with Schizos laying in the corner of a shop with my name on the plastic and I was actually just curious about something for future reference if I decide for another ski.. I've been on a 62 waist then a 69 and now I'm jumping to 85 so I can play in the pow a bit and have the whole 1-ski-quiver thing, I'm just wondering though how does a fatter ski act? I know 85 is definitely not FAT but if I went fatter, for more back country/line ducking, what is there to expect? My mind says slower edge to edge. But idk, opinions? Thanks!