PS This might help -
http://en.wikipedia.org/wiki/Bicycle...f_light_wheels
The advantage of light bikes, and particularly light wheels, from a KE standpoint is that KE only comes into play when speed changes, and there are certainly two cases where lighter wheels should have an advantage: sprints, and corner jumps in a criterium.[15]
In a 250 m sprint from 36 to 47 km/h to (22 to 29 mph), a 90 kg bike/rider with 1.75 kg of rims/tires/spokes increases KE by 6,360 joules (6.4 kilocalories burned). Shaving 500 g from the rims/tires/spokes reduces this KE by 35 joules (1 kilocalorie = 1.163 watt-hour).
So, 35J compared to 6360J - about a 0.5% change in performance. And the numbers would be worse for a Clyde.
So, really - forget about tyre weight and worry about the rubber compound used and rolling resistance. The better makers will give you a realistic speed rating that lets you compare their tyres inside their own range.