I've always run my best pace for any race, invariably always beat runners who are just as good and quite a few times beat runners who should be much faster.
Vladamir Kuts wrote an excellent article about "the record tactic" of racing, in "Run, Run, Run" by Fred Wilt. He describes going to the line against another Russian (before Kuts reached the top ranks) who was much better than him timewise and had many superior performances. Kuts was surprised when the other runner tucked in behind, content to rely on his kick. However by then Kuts had stolen the race, in another personal best time and achieved the championship standard.
Kuts' feeling is that the record tactic is the most progressive and best tactic for racing, that the competitive tactic might win a string of low key races but is not progressive and is likely to fail in top competition. It is notable that most all of the top runners have utilized the record tactic for their races.
Vladamir Kuts, Peter Bolotnikov, Ron Clarke, Gerry Lindgren, Herb Elliot, John Landy, Gaston Roelants, Buddy Edelen, Derek Clayton, Abebe Bikila, Morceli, El G, Carlos Lopes, Steve Jones, Komen, Tergat, Geb, Bekele, Shaheen, Wanjiru ....