Hi Draculav, thank you for your input!
I went down again today to have a look again at the rock, together with two other more ideal cut diamonds for comparison:
GIA 6252007591, HCA 1.0, S$3,599 (Seen through the idealscope and H&A with my own eyes. Everything is perfect!)
0.44c
55% table
61.2% depth
34 crown
40.8 pavilion
GIA 3275403520, HCA 1.3, S$? (should be around the same price range since I asked for TIC diamonds within $3,500 +/- $200 for comparison).
0.51c
57% table
61.2% depth
34.5 crown
40.8 pavilion
Before that, here are the Hearts and ASET picture taken from my handphone. Not the best quality (handphone camera not dead centre) but gives a rough idea of the cut and light performance for the original rock that I chose. The specks on the hearts are just dust and dirt.
My fiance went down with me since she wanted a more fiery diamond, but when she saw the HCA 3.4 stone, she was impressed by it. Let me explain our observations in comparison with the more ideal cuts.
Our HCA 3.4 stone I will refer to as 60/60 and the other two as ideal cut diamonds.
The stone looks bright and "big" due to the 60 table and 59.4 depth. Simply just bright and white. The ideal cut diamonds looks sharp and clear with more contrast. Tested the fire and scintillation in the shop, outside the shop and under the sun. The 60/60 produce really powerful white flashes along with fire. Scintillation is not as good, more like kallang wave with tighter spaces in between each fire spot (since each spot is bigger), but still the white is really bang! I need not say about the ideal cut. Strong sharp, powerful and intense fire spot, very defined and blinking off and on like LED lights. It lacks the 'volume' of white light seen in the 60/60 in a sense that each flash doesn't light up the diamond as much.
Tilting the diamonds around, it is much easier to trigger the scintillation on ideal cut probably due to the larger crown surface area. The firing is very quick and frequent. The 60/60 feels 'slower' as it requires much bigger movements to trigger it, but just a bit more, totally negligible though. The fire from the 60/60 is not as strong, more pleasing, subtle and gentle to the eyes since the white light 'suppresses' it (less refraction actually). Each sparkle from the 60/60 consist of white light then gently split into the colours, like 70% white light then falloff to colours in the other 30%. It is a really different feel from the ideal cut, more dreamy and soft as the white will partially take on the hue of the colour being refracted. As an analogy, 60/60 looks like the initial bang of a firework, ideal cuts are like the glittering after-effects.
In the end my fiance picked the 60/60 over the other ideal cut diamonds. Since we were able to see and compare the diamonds visually, I guess the HCA is not as critical. It still boils down to what your eyes like to see at the end of the day, the overall feel and perhaps the personality of your partner. You can download the AGS Proportion Chart (crown/pavilion) with respect to table% and compare where the cut is in. Mine lands in Ideal for 60% table cut but overall AGS proportion score is borderline 1-2. With so many systems out there, it really can be a headache and a pain to look through and scrutinise all. HCA score of 2-3 really can be considered provided you can see the rock physically. However I would like to add that my observations are for 0.4 - 0.5 carat size diamonds. I did not compare big diamonds. I'm assuming that the effects will have an observable difference between the 60/60 and ideal cuts for larger sizes. Can the ring perform better? Technically yes. Value for money? There are better alternatives. Overall feel when your partner see and like it after comparison? Priceless. All numbers and charts will out the window. Case close happy man.