K kallistibrc Member Joined Jun 26, 2013 Posts 15 Jul 25, 2013 #21 Digerati said: I'm going to go ahead and install the other Radeon HD 5800 Click to expand... Remember, graphics cards are often the most power hungry devices in our system, often much more so than CPUs. So you MUST ensure your power supply is capable of supporting the added demands BEFORE installing that power hungry card. Click to expand... 1000 watt power supply in the machine thankfully. :) So it turns out, that the issue was in fact NOT fixed. I've been wrestling with it for awhile again but didn't want to spam the boards with more false positives etc. I DID finally resolve the issue though. Wow. Turns out that the video card was *obliterating* the system event log with all sorts of REALLY helpful information. Hundreds of event logs, per second, all saying "UVD Information". Basically DRM for video content. This is a bug with ATI cards that has existed since around 2011. Perhaps before. Newer driver releases were SUPPOSED to fix it, but the issue still creeps up a lot. On some machines, apparently, it causes no issues. Others the problem manifests in different ways. Sometimes it's a hard crash of the video card, os, etc etc. In my case, the DPC latency goes through the roof. It also makes sense that it was showing as a result of the HD controllers because it's thrashing the operating system HD (hence why it didn't matter what controller I put the HD on). Long story short, disabling this log spamming has fixed my issue. There are a few different ways to disable it, heres one: Twig's Tech Tips: ATI: Disable spamming of system event logs by ati2mtag DVD_OV UVD Information Thank's again for all your help, and hopefully this info can be of use to other people.