"Much faster" is a pretty squishy statement. Your overall average speed door to door will probably be 1-2 mph faster on a road bike vs. hybrid. Over 10 miles, this translates into maybe 5 minutes. If you have lights and traffic to deal with, any speed advantage can be negated.

More important is to get a bike you are comfortable on, road or otherwise, and if you plan to commute in all weather, this means a rack and fenders are almost a necessity. You may think a backpack is good now, but on a hot day, having that pack on your back is awful. In the rain or on wet roads, fenders make a huge difference. So, even if you don't start out with a rack and fenders, you'll want to make sure the bike will accomodate both.

Also, a frame that will take wider tires is another factor. You may start out thinking fast, skinny tires are nice, but when the weather turns nasty, a wider tire is great.