Near the end of a time trial I noticed my HR getting up to 182, which is very, very high for me. (During a max test 10 years ago in college I got it up to 184, but never higher.) Everyone talks about VO2 max pace being somewhere between 3k and 5k pace, and if so it seems like your *average* heart rate during a 3k or 5k would tell you something about whether you were working at VO2 max pace. But what about the spike you hit toward the end of a race? Should it be close to your absolute max?
When I'm even relatively in shape and I run "hard" I can get within a beat or two of my max. And, yeah, I do it pretty regularly at the end of races.
Depending on fitness level, your "max" can change a little. So, while you will (or should) get very close to your current max at the finish of a 5K, if you take 6mos off and then do repeat quarters (actually just about anything as long as it is not too long would work), you will likely get closer to your "absolute max" (higher).
I reccommend being happy with your current max, and going from there.