With the weight of the XK I definitely recommend the HD coils. I dont think you will need the extra spacer up front. Im running the OME HD coils with no extra spacer in the front and Matt's 1/2 inch spacer in the rear. My XK sits a little higher in the rear now due to Matt's spacer, but I like that stance so I can either load down the rear with Army gear or tow a trailer and still have the XK sit perfectly level with the extra weight. Prior to Matts spacer my XK was level but I hated the way the rear would squat with weight in the back or while towing.

Like you mentioned, OME is the way to go since eventually you will need need new shocks and struts anyways. The HD coils do make the ride a little stiff but I have not heard one member complain about the ride. I myself prefer it to be a little more stiff then the oem suspension. I purchase all of my OME parts from ok4wd.com because they have great customer service, great prices and they are close to me. I can order using ground shipping and its still at my house the next day. They are out of NJ and im located in NY.