I like my touring bike (Sherpa 30); it's very smooth, handles well under load, and has a road triple on the front so it's pretty quick when I need it to be. I picked it over a cross bike because I have big panniers and big feet, I usually carry a fair bit of stuff, and prefer a more upright position on those days when I haven't woken up completely. (Also, the Sherpa was $600 off.)

If I wanted to go quicker, I'd switch to a road bike, not a cross bike. That being said, a road bike would maybe shave three minutes off my commute. I have to stop too many times for traffic, railway tracks etc. so it doesn't matter if I'm doing 35 km/h or 50 km/h, I'll just have to wait longer at the light/stop. Oh, and we pretty much go over every type of terrain short of scree: railbed, ditches, dirt paths, grass, MUPs, gravel, broken pavement and asphalt. I have had no problems with the stock tires (I think they're 32cs but can't remember.)