There is a real difference. On a quality hybrid bike(specialized globe) I made it to work in around 45m-70m. On my cyclocross bike my times are 35m-50m. I havn't tried it on my MTB and I really don't want to. I havn't tried it on my Raleigh either but that thing is slower than my MTB...

A bridge that I crank up in 46x18 on my cannondale, I can fly up in 53x18 on a Specialized Tarmac. Pity the tarmac can't carry anything and can't use full fenders. I think if I actually tried my commute on a Tarmac I could probably make it in 30m. All these times are for about the same amount of effort of course and around 13 miles one way.