While you say you were solo most of the time, don't underestimate how much the little time you spent near other riders helped your time/speed. Even other riders and other vehicles passing on the road help provide a draft to speed a person up some. My times for the 63 mile organized rides where I can stay in a group of at least 3 people are 3 to 4 mph faster than the solo 22 mile rides I do several times a week. And we aren't even trying to go fast on the long rides.