Por-15 is great for things like inside the doors or wheel wells (where the purpose is to build a swimming pool film that won't allow water to linger in the seams...). But I wouldn't use it for the frame, it will be too thick, its not really meant to be sprayed but brushed. Pretty much, you just want the frame to not be ugly--but don't need it to be the center of focus. DP90 will give you the protection and won't look wrong.
For the suspension pieces, I did go with thicker, glossy paint. I only went with powder coating on the front A-arms, but you would probably be happy with the 11 rear pieces (the 4 long rearward rods, the upper and lower A-arms, the torsion bar and the uplinks) with a bit of a contrast in gloss...Lee