Thanks for sharing your context and background. If she likes cushion cut, I'd definitely focus on that. I personally think larger carats look better in fancy cuts and would also look at emerald cut (they are super classic, yet glamourous and chic). Of course, a modern round brilliant is always a great choice too. Ovals are classic, yet look much bigger than other cuts. Based on what you described of her and your social circle, I would recommend looking at colorless and very high clarity stones, unless your girlfriend specifically likes warmer colors. I would stay at D-F, FL-VVS (VS at bare minimum), with no florescence (unless she specifically requests it). Given that you want to optimize your ROI, I would do a lot of research around cut as well. It will be very challenging to find what you are looking for even with your budget as large, well cut, colorless, high clarity stones are rare and hard to find. You can work with vendors to get them custom sourced and cut. Lastly, if her style is very simple and elegant, you can't go wrong with a solitaire, simple halo, or 3 stone. Congratulations, good luck with the search!
Thank you so much for your suggestions, and response.
This question may seem a bit silly but comes from a place of earnest ignorance. If I stick to colorless (D-F) and no lower than VVS2, should I realistically up my budget. I am able to do more, but it feels obscene to spend more money on that when we could use that money for community support, or other social issues, we are fortunate but I do not won’t to be overtly obnoxious. That being said if a good 4 carat Diamond in that color and clarity range isn’t realistic in my price range, I don’t want to be nonsensical while searching either. Thank you again for all your great info. Jeremy