I believe the argument could be made that two a days make as much sense at 90 miles as they do at 50-55 miles. At 90, you may finally be reaching that point where you are maximizing each day's workout. I have no explanation for similar performances on substantially less miles, nor do I think it is pertinent to the discussion of the value of two a days. In our short discussion here we have revealed that there is value in the practice when you have shorter time windows in the course of your day. The additional mileage provided by the second run can only be a benefit to a runner looking to produce the best possible race preformance. I think a disciplined runner would see real benefits on race day from a well structured two-a-day program. My opinion.