more good feature for Pallid to me :
- the pale area on the median covert on the upperwing as shows Montagu's, Hen and Pallid but not Pied
- P5 is not stronly digited and just slightly longer than P6 given the impression that only 4 primaries are digited, on Hen and Pied it should be much more digited and show 5 clearly digited primaries, it seems that on Pied P5 ended at about 3/4 of the distance between P6 and P4 where on Pallid it just reach half distance... I think our bird fit this feature quite well, so to me this rule out Hen and Pied
- starting from P6 primaries are having more pale tip, and it seems that this is ruling out Montagu's...
Having said that I would go for Pallid...