Just my tuppence worth, on a subject I’ve expressed some practical interest in … that is to say I’ve actually made (and play) some relatively wide-bore whistles, so I can post some “real” numbers as examples.
All numbers are “eyeballed” with a tape-measure, so may be +/- a mm or so.
For reference, a “normal” D whistle (12mm brass) is 265mm long from “window” to end … it’ll play 2 octaves without any real effort.
A “normal” C whistle, both Feadog (14mm tube) and Clarke Sweetone (tapered), are 292mm long from “window” to end … they’ll both play 2 octaves without any real effort. I’ve re-drilled my Sweetone to play in D with a low-C, ie a seven-hole whistle … it works 
A seven-hole whistle in D (+low-C) made from 18mm bore (20mm o/d) plastic conduit has a much “purer” tone than any of the above, though this factor is partially mouthpiece dependant, it is 285mm long from “window” to end … it’ll play an octave D-d then on up to “a” … plus the low C, obviously. A “vent-hole” under the LH thumb (recorder style) can help with the higher notes, basically it means you don’t have to blow so hard to get the higher harmonics, so they are of a more similar volume to the lower notes.
A seven-hole whistle in D (+low C) made from tapered 22-20mm bore bamboo has an even “purer” tone than any of the above. This “pureness of tone” is due mostly to the loss of high harmonics, it’ll only just play up to the f# above high d, but sounds beautiful … if a little quiet. It is 255mm from “window” to end, so overall is about the same length as the “normal” D whistle.
A Fitchhorn “Song Flute” (looks similar to a “Tonette”) will play as a “D+low C” instrument with a slight tweak of the fingerholes, (low B if you stop the “bell” with your knee or whatever). It is approx. 25mm o/d, 210mm long from “window” to end, and relies on a LH thumb-hole for the high d. It has no usable high harmonics so can possibly be considered as an ocarina.
I hope these numbers may help demonstrate the extents available, and their limitations … to precis :
Short and fat, lovely “pure” tone but limited range.
Long and thin, lots of “chiff” and wide range (over two octaves, with practice)