This has been pretty well covered on the Whitney Portal Store Message Board - see the topic, The Winners.
Summation: having done both, I think Pikes Peak is harder because it covers a full 26.2 miles vs the Whitney course of 22 miles. Pikes Peak starts at an elevation of 6,300' which is much lower than the Portal starting point. True, Pikes Peak is only 14,115', slightly lower than Whitney.
Final proof: In 1961 Calvin Hansen from Colorado won the Whitney Marathon in 3:54.45 and also won the Pikes Peak Marathon that year in 4:07.15 BUT had Whitney been 26.2 miles this would certainly make Hansen's time way over 3:54 & probably closer to 4:30 + or -. So an argument could be made that if Whitney was 26.2 miles it would be tougher. But since the original question was Pikes Peak Marathon vs MMWT at 22 miles "only" this would in my opinion make the Pikes Peak Marathon tougher.
