I have 20k to spend on an engagement ring. I've been to Tiffanys, Cartier, downtown L.A., and looked at prices on the internet. I basically want a well cut round solitaire on a plain 4 prong platinum setting. It seems that I could get a bigger stone if I didn't buy the ring from Tiffany or Cartier. But the setting seems much nicer at Tiffany and Cartier. So basically, if you had 20k, what would you get? Please be specific about the stone and the setting. Thank you so much.