Sean,
K36 should be mixed 5:1:1 using DT reducer and K201. You don't have to add reducer but it will help it flow and keep it open longer. Use DT885 if it's about 75 degrees when you spray.
K38 is a high build primer and does mix 4:1, I've never reduced it, and the P sheets for it don't say anything about reducing it.
The K36 is more of a surfacer than high build (although it still builds nice)
The K38 will definitely go on heavier and require more sanding, the K36 with 1 part reducer will flow out nice and smooth and make sanding before paint a snap.

The size of your gun tip will also make a huge difference, I use a 2.0mm tip on my Sata KLC, smaller tips will make it go on drier in appearance (more orange peel) unless you reduce it further. For air pressure I use 29psi. I wouldn't use anything smaller than a 1.8mm tip for spraying K36 and wouldn't use smaller than a 2.00 tip for K38. PPG recommends a 1.4 to 1.6 fluid tip, but I've found the nicest coverage with the 2.0, keep your passes quick and smooth and it add's very little weight.

Jeremy