thermostat question

ok dont know what the temp was at cuz I only have a dash guage in it and no overheating light came on. I have no bleed hole in it. I have ran this car for several years now and have not had a problem. hat is why I am going with an over fill thought. My question now is why the 2 different opinions in the degree of thermostats, I was thinking of a 160 so why not. what would be the different in 160 or 180. I would think the 160 would open quicker and cool it down faster. And what is the importance of a bleed hole. If a bleed hole is so important, why dont they put one in it from the factory. Just questions guys. I put the overflow bottle at the 2 qt. level. Maybe it should have been at the 1 qt. level. talk to me.