For our power, temperature, clock speed, and fan speed testing, we use Powenetics testing hardware and software. We capture in-line GPU power consumption by collecting data while looping Metro Exodus at 1440p ultra as well as while running the FurMark stress test at 1600x900. Our power testing PC uses an open testbed, as that's required for all the extra wires and riser card, and it's the same old Core i9-9900K that we've used for the past several years.
We tested the PowerColor card in both OC mode and Silent mode, powering off the PC in between mode changes. The only differences appeared to be in fan speed and GPU temperatures, with clock speeds, power, and performance remaining mostly unchanged (within the margin of error).
First things first, note that the power use of our sample RX 6600 XT card was significantly higher than the reference TBP (Typical Board Power). The 6600 XT was supposed to be a 160W card, but AMD sent us an ASRock Phantom Gaming D that looks more in the 215W range. That helps to explain some of the lack of performance differences earlier, not that it really matters now that the RX 6600 XT has officially reached end of life.
Clock speeds for the 6650 XT Hellhound are right in line with the advertised boost speed of 2589 MHz while gaming, just a bit below the RX 6600 XT. Clocks drop about 200 MHz with FurMark, though GPU power use hardly changed at all.
The fan speeds and temperatures on the Hellhound are perhaps the most interesting aspect of the design. In OC mode, temperatures stayed below 65C while the fans spun at about 2,000 RPM. On the other hand, silent mode limited the fan speed to around 1,400 RPM, with a temperature target of around 72C.
We measured noise levels at 10cm using an SPL (sound pressure level) meter aimed between the two fans. That helps to minimize the impact of the CPU cooling fans, and the noise floor (with the CPU fans running) of our test environment and equipment was <33 dB(A). OC mode resulted in fan speeds of 42% and 44.9 dB(A) noise, while silent mode dropped the fan speed to 35% with just 39.0 dB(A) — a very good result.
We also set the fan speed to a static 75%, just to see what the card might sound like when it's heavily overclocked. It reached 60 dB(A), which wasn't particularly good, though people should never see such high fan speeds during normal use.