They're comperable in price to the Purolator Boss if you bulk order 6 or more from Royal Purple direct, but it appears that the free shipping threshold is now $100, I thought it used to be $50 or $75.
What vehicle are you using them on?
Is the XG3600 size filter the original size or did you already cross reference an oversized?
If XG3600 is the original size and you've got the space for extra diameter you could always use the XG8A.
My application calls for a MC-910
The larger size is MC-400
I’ve always gone for the larger filter if I have a choice
My car calls for 5.9 quarts of oil so the larger size works out for a close 6 quart drain and fill