i would go with 10w30 mobil1 full synthetic.
http://ecx.images-amazon.com/images/I/41zNAQR%2BZEL._SL500_AA280_.jpg
is what i use although its really expensive its like 6 or 7 dollars a quart.
id go with 10-w-30 in it,that's a good weigh oil to use in that car,and it will be the best for it,royal Purple is a good oil but not as good as mobil one is,but id use 10-w-30 in it,this way it wont change anything in it,good luck and merry x-mas.