Tire pressure/speed

Weight of the rider?  Someone that is heavy might take a long time on the 60 psi as it would likely pinch flat on the first pothole they hit.  

yes, at 170 lbs i would recommend around 100-105 psi on 23mm tires

this question is unanswerable without a ton of information and a ton of physics. it also doesn't matter. do it correctly and then you don't need to find the answer

whats the roughness coefficient of the course.  whats the actual width of the tire, whats the width and contact area of the tire under loading at each discrete pressure value in your selected range.  what is the average speed of the racer, what is the median speed of the racer as described by time traveled at that speed.  what is the external barometric pressure, what is the temperature of the tires, what is the ambient temperature, what is the temperature of the road.

and with that you can find the rolling resistance and calculate the traveling speed at a given power.

do that for a set of power values

now do this for every different type of tire and you can find your answer

it isn't a question worth answering accurately

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If your tires are really under inflated you are going to feel like you are riding though mud.  I did two 45 minute rides with the tires at about 45-55 PSI (no pinching flats either since I didn't go over anything too bumpy).  I averaged 16 MPH.  Then I made some adjustments to the fit (it was a new bike) which involved raising the seat height and raising the seat angle.  The following ride with the seat adjustments and tires inflated to 90 PSI I averaged 17.2 mph over a 90 minute ride. I think a lot of this had to do with the seat adjustment, but the tires were rolling noticeable better too. I didn't feel the bike slowing down every time I eased off the pedals.  It actually would coast and maintain speed when I eased off the pedals.   :-)

On rough country roads (the majority of what I ride on) I find that tire pressure that is a little softer (90 psi-100 psi) is a lot more comfortable than higher pressure (110-115 psi).  When the pressure is high I can feel every bump in the road and I actually have slower average speeds than I do for lower tire pressures.  For me I seem to ride slightly faster (0.1-0.2 MPH) faster on tire at 95 PSI than I do on tire at 105 PSI over my standard morning ride.  I usually just set the front tire somewhere between 90-105 PSI and set the back tire at 5 PSI higher and don't worry about it to much.  In an event I don't know the course as well as I do my morning route that I do multiple times every week so trying to guess what pressure is going to be the best for the road surface of the race isn't possible so I just go for comfort and don't fret the 0.1 mph difference that tire pressure could make.  

Exactly! This was tested and publicly noted years ago with a chart by a well respected engineer Tom Anhalt. Here's the chart showing what happened in a real world scenario for rolling resistance vs. increasing PSI (blue diamonds) for one set of tires. Note the sharp shift upward in rolling resistance after ~ 120psi that occurred.

Again don't always believe what you feel!