Bacciagalupe

Let's assume your road bike is 20 lbs, your touring bike is 28.

On the flats, there is practically zero performance difference due strictly to weight.

On a 5% climb that is 1 mile long, theoretically that extra 8 lbs will add a mere 17 seconds to your climb, and costs an extra 4 calories.

The more likely explanation for the speed differences, real or perceived, between the two bikes is:
• The road bike is set up for faster turning and responsive handling; the touring bike is designed for stability while carrying a load. That plus the weight difference makes the road bike "feel" zippier without really producing an actual performance improvement.
• The touring bike likely has wider tires with more tread, and are made for comfort and flat-resistance. The road bike almost certainly has skinny tires made for speed. This will produce both an actual (albeit small) and perceptual speed change.
• It's possible, if not highly likely, that the road bike has a more aggressive rider position than the touring bike. If you are more upright on the touring bike, that will increase aerodynamic drag and will slow you down.
• As long as you expect the road bike to be faster, you will always find a reason to believe the road bike is faster. (Expectations and confirmation bias have a very strong unconscious effect.)

There is a separate issue, in that if the road bike feels faster but has a harsher ride, it is possible that over longer distances (70+ miles) this may slow you down due to increased fatigue.

Keep in mind that [url=http://www.pponline.co.uk/encyc/speed-cycling-how-reducing-your-drag-will-improve-your-cycling-performance-41267]"aerodynamic drag increases as the square of velocity; if you double your speed, you will expend 4 times the energy to overcome drag."[/quote]

I.e. drag, not weight, is the primary mechanical factor that will affect a bicycle's performance.