I don't think you can do a snap judgement and say "oh that's a 150" or "that's somewhere in the 160s'. To get that fine on score you have to take the spotter and start to add up inches.
I think the best way to quick judge is too look for outstanding features. If the standard 155 buck is 20 wide, 20 inch beams two inch brows, 14 inch G2s, 8 inch forks and average mass, and the buck you are looking at has huge front forks, add 10 inches, if the fronts are poor subtract 10 to 15 inches. If you know what the standard 150 buck or 160 buck looks like and you do this enough times and you will get in the ball park. For example I saw a nice buck this fall, Standard 155 buck, but real big browtines, better than average mass and some NT points pushed him up to the high 160's gross.