Here are the two stones. To keep it simple assume the color and clarity are eye clean and colorless on both, both have excellent polish and symmetry, and both prices are approximately the same (within $200).
1.27Ct
Table 57
Depth 61.9
Crown angle 35.5
Pavilion angle 40.8
HCA 2.6 VG VG VG VG
AGS Ideal range (per the charts linked below)
GIA Excellent Range (per the charts linked below)
Versus
1.3Ct
Table 57
Depth 60.9
Crown angle 33
Pavilion angle 41
HCA 0.9 Ex Ex Ex VG
AGS Ideal range (per the charts linked below)
GIA Excellent Range (per the charts linked below)
The first stone's angles dont seem to be "complimentary" and the second stones angles are both shallow. However per GIA and AGS they both are Ideal/Excellent based on their charts.
AGS Guidelines - http://www.agslab.com/docs/pbcg/AGSLProportionCharts.pdf
GIA Guidelines - http://www.diamondcut.gia.edu/pdfs/booklet_cut_estimation_tables_highres.pdf
How to pick which is better as far as light performance given other things are equal?
1.27Ct
Table 57
Depth 61.9
Crown angle 35.5
Pavilion angle 40.8
HCA 2.6 VG VG VG VG
AGS Ideal range (per the charts linked below)
GIA Excellent Range (per the charts linked below)
Versus
1.3Ct
Table 57
Depth 60.9
Crown angle 33
Pavilion angle 41
HCA 0.9 Ex Ex Ex VG
AGS Ideal range (per the charts linked below)
GIA Excellent Range (per the charts linked below)
The first stone's angles dont seem to be "complimentary" and the second stones angles are both shallow. However per GIA and AGS they both are Ideal/Excellent based on their charts.
AGS Guidelines - http://www.agslab.com/docs/pbcg/AGSLProportionCharts.pdf
GIA Guidelines - http://www.diamondcut.gia.edu/pdfs/booklet_cut_estimation_tables_highres.pdf
How to pick which is better as far as light performance given other things are equal?