Nice pic, love the coloured LED on the cooler. Gives a little bling without being too flashy. Also that's a Noctua case fan I see there, a man of good taste
The extra 16GB you say is coming, is not needed and won't really do anything at all. but hey, it's your money!
IDK what John Chesterfield is on about, you said in your very first post that you have an RM750, so you have the perfect PSU for any 30 series card. But yes, for sure your PC can definitely "handle" an RTX 3060 or 3070 with a 750W top tier PSU, a 4790K CPU on a Maximus VII and 16GB RAM. Those cards would be very happy in that system. I probably would not get a 3080 or 3090 as that would be a slight waste with that CPU.
Would the card be happier with a much faster...