so, perhaps my question should have been rephrased, "how much faster...if any, are recumbent bikes than trikes?" ...
My reason for thinking at the top end trikes were as fast as bikes is that the other week when i did the BHF charity ride i was quite surprised that my 'terminal velocity' on the road (the snake) on the MTB with its 2.5", 20psi tyres was about 42mph, almost exactly the same as what it is on the roadie. I was expecting it to be less. Which proves, that at the top end when you're ragging it down a hill, rolling resistance of tyres doesn't make a blind bit of difference, it's all wind resistance.