I have a 7500 and a road-bike, and find that the difference in speed is totally dependent on the amount of wind. For "general" conditions, I find I'm 1-2 mph faster on the road-bike. In heavy head-winds, I'm 5-7 mph faster. The big difference for me is the difference between the upright riding position and the more aggressive road-bike position. However, I'm quite a bit slower than you to start with, so I don't know if the same speed changes would apply to a faster rider.