Based on Pulsar website the following figures are quoted for Horizontal Field of View (FOV) at 100m:
XD19s 50.5m XQ19 34.4m
XD38s 25.0m XQ38 17.2m
XD50s 19.2m XQ50 13.0m
So effectively the new XQ38 has a narrower FOV than the older XD50s model.
Comparing the XQ50 directly with the XQ38, the XQ50's FOV is approximately 1/3 less, which is quite significant.
I agree that ideally the best way would be to compare both units in the field, but not many people actually get the chance to do this.
Based on known XD38 performance, if planning to mainly use in woodland environment I would go for XQ38 over XQ50.