You're definitely right on perspective.
So, I'm on hour 21-22 now and I just got done running some really stressful processes in Photoshop and Illustrator as a test. I took a look at my Console after a while, and to my dismay, I saw my first mDNSresponder "ticks" message. Ugh! I know now that it's all going down from here. This is the thing that I never want to see because as soon as it happens, the mouse gets rough. It's the same way you describe it Ian - not exactly jerky yet, but rough - though, if I leave it this way long enough it will eventually get jerky. So can you do me a favor? Can you look in your Console, make sure "All Messages" is clicked over on the left, and then do a a string search for "ticks" and see if anything comes up? I really hope we can at least find a common ground with that message if nothing else. That's my last hope of finding any explanation, though I don't even know what the "ticks" message means in terms of what's actually causing it other than system overload.

EDIT: I was thinking of building an Intel also, once I get some more cash. Thinking about using a GA-P35-DS3L for the board. What about you?