Interesting... I ran this DPC latency checker, and got a latency spike every 60 seconds - just one bar's worth of a spike.
Coincidentally, my Easy tune is set to update itself every 60 seconds. If I close Easy Tune, the DPC spikes go away.
Not sure if this actually affects anything; I leave Easytune running because I use it to control my PWM fan, but... maybe I'll run some benchmarks and see if there is actually any negative effects to the DPC spike.