I'm absolutely sure Dr S has very good reasons for recommending a 90 minute mash, he would have thought about it, he even knows what is happening in the mash and still recommends 90 minutes. Sort of makes your question redundant and very much gives then impression you know better.
kadmium have another read of what Palmer has to say, mind you a 1 page precis of the mashing process is going to be far from complete. If you want a better (free) read on
Starch Conversion, visit Braukaiser I really think its much more helpful than the little Palmer spent on the subject.
Around 90 minutes is the point of diminishing returns, 60 minutes is a fair compromise but you will get less extract and probably a higher FG and increased randomness. I find most of my mashes end up being around 80-90 minutes including ramp times.
If the regime is rising from a Glucan or protein rest closer to 90 minutes for the time between 60 and 80oC
In what is closer to an Isothermal mash, again including ramping to mash out closer to 80 minutes.
Those are compromise times, I know I could get a little more out of my mashes but am fairly happy with brewhouse efficiencies, without pulling any tannins, which I find starts to happen if its pushed much over 85% overall (in fermenter).
Mark