... IMO, the 5970R is one of the nicest Patek, in the nicest metal... Basically its my grail watch. Closest as possible to perfection. You seem to agree with me on the warmth of the RG, and how this watch is a step above the YG and the WG. Point is : How to let go such a beauty, in favor of another, while ur so convinced of it?
I would compare the Platinum to the WG... and even then i find the WG a notch above, nicer , more readable dial, that allows u to switch different colours of strap ( thanks to the white dial ).
Personally, i wouldn't go for it even if i jst like. I would ask myself, why to go for it? Is it jst because i got kind of used to my RG and i am tempted by something "new" that is also nice but has something , i don't know what, that jst don't feel as right as what i have?? You might need to ask urself, how will u feel after owning it for a while?
Another important thing, how did u feel better getting ur RG?
When u will be sitting in front of ur AD, with ur 5970R on the table, and u will have to leave it behind along with a big check... how would u feel?
If its an investment issue, and u really like the platinum, and of course if u can afford it, i would take it and keep the RG, as they still look different
Still, nice dilemma, even if i wouldn't take too long to decide 
Thanks for sharing
Karim