importdata() for large number of .txt files is veeery slow. How to improve it?

I use the simple code below to create a 3D Matrix out of a bunch (e.g. 200) of txt files. Despite preallocation it takes quite long.

a = dir('*.txt');
Image=zeros(960,1280,200);
for i=1:length(a)
 Image(:,:,i)=importdata(a(i).name);
end

Is there a way to speed it up? I know for example that the individual numbers are in 16bit UINT format, maybe that information could be used? Alternatively, I could produce smaller .tif files instead of .txt, in case the matlab image read functions are faster...