I sent my camera back to ZWO to have the v1.3 board upgrade done. Tonight I finally got a chance to take some dark frames to compare the difference in amp glow between the two versions.
The last set of darks that I took with my '224 was a couple months ago. I used the same exposure and gain settings, and the same dark frame generation method in DSS. Given that, these still aren't a complete apples-to-apples comparison. The v1.2 dark used 14 frames, and the sensor temperature was 12C. The v1.3 dark uses 20 frames at a sensor temperature of 29C. So if anything, the new version is at a slight disadvantage due to the higher sensor temperature. I believe you can see the effects of higher sensor temperature on the increase of noise (hot pixels) in the v1.3 dark.
Both darks are 60 second exposures at a gain of 200. I performed identical linear stretches to both darks to bring out the amp glow pattern.