Elven Characteristics

[Galin]

The second statement is more concerned with a minimum height.

I might agree except that the second statement adds that 'some' of the great kings and leaders were taller... taller than what? The only reference number here is 6 foot 6, and as one could reasonably expect some Elves to be taller than 6 foot 6, that leads me to think that Tolkien means 'some' of the great kings and leaders were notably taller than 6 foot 6...

... but to me that doesn't seem to mesh well with the other statement, in which it is generally noted that the Eldar and especially the Noldor were normally about 7 feet tall...

... as that's notably taller than the reference number in the other quote [a half a foot taller], and there it's not 'some' great kings and leaders, it's the normal height of the Eldar in general, a rather sweeping reference, even if we have more Noldor with 'especially'.

That's why I tend to think Tolkien may be working with different ideas in the two, noting also that in a text likewise written in reaction to artwork by Pauline Baynes [which thus can be paired with the 6 foot 6 quote], Elendil appears reduced [if compared to the 'rangar' description in Unfinished Tales anyway] from being nearly 8 feet tall to a 'mere' 7 feet tall.

Tolkien might have 'realized' for Thingol [and possibly other great Elves] to have been taller than Elendil he might have to shorten the conceptions up just a bit.