As you've likely guessed, vertical concatenation of 1600 arrays results in at least 1600 files from tall/write. This is the case because tall/vertcat is conservative, it assumes all input argument are truly tall and avoids combining multiple input arguments into the same partition (and so file). I'm afraid there isn't a direct way to reduce the number of files.
I am surprised this causes the program to crash. Would it be possible to hear some more details about this?
If the order of data is not important, and you are working with R2018b, there is an alternative. You can stack data by interleaving rows with matlab.tall.transform:
tX = tall(..)
tY = matlab.tall.transform(@reshapeToWidth5, tX);
function y = reshapeToWidth5(x)
y = reshape(x', 5, )';