Cesar, I think Magill's suggestion applies well if you're in the middle of a pack or running a large race where there are a lot of runners around. If you play surging tactics to go after one runner, you might get that one runner. However, in doing so, you might lose the opportunity to pass 5 or 10 other runners in the steady stream you're running in.
Personally and I hope this nobody takes this the wrong way but I don't often find myself in this scenario (Chicago Marathon being a notable exception). I'm typically in an area where the crowd has thinned out quite a bit and I find myself facing head to head battles against one or two runners more than in a mass of runners where a steady pace will lead to passing more runners. Even if one is in this steady mass, though, I'd argue that focusing on how you feel is more effective than splits. Same scenario, you're feeling great but your splits say you are going “too fast”. What do you do?