Matlab imwarp over 3x faster than imtransform

Matlab R2013a introduced imwarp(). R2013b Lint warning tells you to use imwarp() instead of imtransform().

For a simple test (a horizontal linear shift) imwarp() was 3 times faster than imtransform()

bg = imread('myimage.jpg');
[nRow,nCol] = size(bg);
for ....
if ~oldWay % newway: Matlab R2013 and newer
  tform = affine2d(T);
  RA = imref2d([nCol,nRow],[1 nCol],[1 nRow]);
  data(:,:,i) = imwarp(bg,tform,'outputView',RA);
else % old way  Matlab R2012b and older, and Octave
  tform = maketform('affine',T);
  data(:,:,i) = imtransform(bg,tform,...
                  'Udata',[1 nCol],...
                  'Vdata',[1 nRow],...
                  'Xdata',[1 nCol],...
                  'Ydata',[1 nRow]);
end %if
end %for

% oldway: 14.30 sec. octave 3.8.1 using 1 CPU core
% oldway: 14.24 sec. R2013b using 4 CPU cores
% newway: 4.19 sec. R2013b using 1 CPU core

Note how Octave is as fast as Matlab imtransform, but Octave only uses 1 CPU core instead of 4!