What is the correct sized Snowspeeder to pair with the UCS AT-AT (75313)?
From Brickset: "The vehicle measures 62cm in height and 69cm long".
The same measurements of a real AT-AT would be 22.5 meters and 20 meters.
Therefore the 75313 is scaled between 1:36 and 1:29, depending on whether the height or the length is more important.
A model of the 5.3 meters long Snowspeeder at these scales would be anywhere between 14.7 and 18.2 cm long, so the 75259: Snowspeeder – 20th Anniversary Edition at 18 cm would definitely be in the correct scale range, and it has a passing level of details as well.