Cut...what gives?

From my research, I determined that not all diamonds that are graded excellent (ideal) cut from GIA or ASG respectively are actually an excellent (ideal) cut. I have also realized that the criteria for grading cut have been evolving dramatically over the years. My question is if I have a diamond that is graded excellent (ideal) from GIA or AGS, and it received a score of 2 or below on the HCA calculator and looks good under an ideal scope how much more information should I obtain in reason, to make sure that I am truly getting an excellent cut stone? Do I really need to get a sarin report to verify the angels the cert? Do I really need to do all those others tests like the brilliance scope, diam calc...ect.

I truly want the best cut stone that I can afford, but I feel that I've been doing so much research online without actually seeing the diamonds in person that I might be going overboard on trying to select a beautiful stone. In my mind, I feel that by doing all of this research and getting a stone that meets the above criteria that the stone should look great in person. But at what point does all of this research become academic and the diamond would still look good to me in person? For instance, if the diamond specs looks good on the HCA (under 2) and the ideal scope is good but the diamond’s specs are different between the sarin report and the GIA cert due to the GIA rounding, will it really make a dramatic difference on how the diamond looks in person to me. Please help.

Okay heres the deal. I'm a first time diamond buyer trying to sort out how to evaluate an excellent cut on a diamond. Prior to a couple weeks ago, I had rarely paid attention to diamonds at all. However, now that a diamond purchase is on the horizon I decided I needed to educate myself a bit and do my due diligence to get the most beautiful stone for my girlfriend.

I'm looking at buying a round, excellent cut, diamond around 1karat. I have a good understanding of where I want to be on color, karat, clarity as well as price....my only problem is cut...it's so confusing.

From my research, I determined that not all diamonds that are graded excellent (ideal) cut from GIA or ASG respectively are actually an excellent (ideal) cut. I have also realized that the criteria for grading cut have been evolving dramatically over the years. My question is if I have a diamond that is graded excellent (ideal) from GIA or AGS, and it received a score of 2 or below on the HCA calculator and looks good under an ideal scope how much more information should I obtain in reason, to make sure that I am truly getting an excellent cut stone? Do I really need to get a sarin report to verify the angels the cert? Do I really need to do all those others tests like the brilliance scope, diam calc...ect.

I truly want the best cut stone that I can afford, but I feel that I've been doing so much research online without actually seeing the diamonds in person that I might be going overboard on trying to select a beautiful stone. In my mind, I feel that by doing all of this research and getting a stone that meets the above criteria that the stone should look great in person. But at what point does all of this research become academic and the diamond would still look good to me in person? For instance, if the diamond specs looks good on the HCA (under 2) and the ideal scope is good but the diamond’s specs are different between the sarin report and the GIA cert due to the GIA rounding, will it really make a dramatic difference on how the diamond looks in person to me. Please help.