I have noticed that some years ago a measurement was made to compare the percentage of a lap on full gast at the same rider's 600cc- and 1000cc-bikes. On a 600 it was full at 75% of the lap and on a 1000 only 15% of a lap. Which means , for my eyes, that the modern big bikes already are too fast for the circuit. Of course a bike with a lot of power can accelerate better to get a higher speeed and shorter lap time, but with a higher speed one have to brake earlier for the coming corner. My conclusion is that the faster speeds around the TT course now , are depending of less bumps and straightend corners. Some gain, but not as much, because of tyres, brakes, stronger engines and better suspension.