Futuremark adds new test to its 3DMark software. The new benchmark called Fire Strike Stress Test will test the stability of the frame rate in selected number of loops of Fire Strike. Technically this benchmark could be named throttling test, since the final score shows how stable is the frame rate of the best run compared to the worst.
New benchmark is available for Advanced and Professional Editions of 3DMark. Professional Edition allows up to 5000 loops and testing in window mode.
Stress Test will monitor the frame-rate, GPU and CPU temperatures and CPU frequency. Surprisingly it does not monitor GPU frequency and GPU Load does not seem to work for my R9 390X: