The problem is most 10Ks are usually associated with another race and end up as the less-competitive alternative. In the local 5K/10Ks, maybe one fast guy runs the 10K (winning in the 36's) and the rest run the 5K (winning in the 16's). In the big local and regional races, the HM is most competitive and the 10K is the afterthought. Local HM (~700 runners) won in 1:10-15, with 36-something winning the 10K and maybe 3 guys breaking 40. In the bigger regional race, with 7000 runners in the HM and people flying in to win in 1:06, there are 6000 runners in the 10K. Winning times in the 33's, and 36 might get you on the podium + prize money.