Thank you for sharing your results, Steve.
I approached my tests with an end user perspective. Datacolor claims a 55% improvement in low luminance accuracy. I had no means to measure this difference, but real world results were close enough to i1Display Pro to make me believe it. Using the OEM software, I noticed a good improvement in shadow detail, with less banding than Spyder4. Argyll CMS is not yet optimized for the Spyder5, I assume, so the calibration process takes hours, but the final results are very good. Again, not much to complain when compared to the i1D3.
What threw me off were some wacky results with lower quality TN displays. For example, on a 2011 13" MacBook Air, the OEM software produced a completely unusable profile, with compressed and uneven gamut. This happened when aiming for 6500K or native white point. Super strange. I still haven't contacted them about it.
In any case, I wouldn't recommend anything other than the Express version. On the higher price points, the X-Rite units deliver better results for a lower price.