A quick update:
I've pinged Hexus to ask if they'll reinstate DPC testing (August of 2015 seems to be the last time they published it).
HardOCP includes it in their reviews, they might include extra comments/stats with supplied software/utilities installed as well, suggested search string: "DPC latency" +"motherboard review" +170 site:www.hardocp.com The DPC info is usually on the review's Subsystem testing page.
AnandTech also has it, usually on the System Performance page with a comparison graph, search string: "DPC latency" +"motherboard review" +170 site:www.anandtech.com Example graph: http://images.anandtech.com/graphs/graph10294/DPC.png