Assuming you can clip into the Zeros (I had an intensely difficult time doing so, despite numerous adjustments, as did many other women; thus the "light action" version was born), you should be able to sprint easily in them. You can adjust the float down to a level that works for you.
I used X-2's, which have unlimited float, for years, and they did have that "ice cube" feeling. For me, that made it a bit harder to sprint, and I felt like I lost power. In fact, DH could tell I was faster and more confident when I started using the Zeros (when I was able to clip in, that is). I much preferred the stable feeling of the Zeros, and they did give enough float for my knees...I just couldn't clip into the darn things! So I sold 'em and went with Eggbeaters Candies.
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow