Advertised specs are meaningless. There is no industry standard for measuring response time, or contrast ratio, or anything like that. Which basically means the manufacturers can advertise any numbers they want. They will run their monitors through all the different tests that they have, then advertise whichever one has the best result, even if it's not representative of real world performance. This means that specs like response time cannot be compared between manufacturers because it becomes apples and oranges. You can't even compare specs from two different monitors from the same manufacturer, because there's no guarantee the results were achieved the same way.
The best thing to do is to have some faith in reviewers, and mostly in your own eyes.
Also, you generally get what you pay for. If you were to compare a 1080p monitor with a 2ms GtG and 50000:1 contrast ratio for $150 bucks, with another monitor with the exact same specs that costs $300, chances are VERY high that the more expensive monitor will look and work much better. Thus proving that the advertised numbers count for nothing.