SPM - test slice vs volume

Results from code below (115 fMRI HCP files)

Vol - read
Elapsed time is 4.536723 seconds.
Slice - read
Elapsed time is 4.581537 seconds.
Vol - read and write
Elapsed time is 8.776489 seconds.
Slice - read and write
Elapsed time is 71.972148 seconds.

function cspm_test_spmreadwrite ( P1, P2 )
    % Testing reading and writing by slice vs volume
    % Copy same files into two different folders
    % Select each set of files (P1, P2)
    V1 = spm_vol(P1);
    V2 = spm_vol(P2);



    disp('Vol - read ')
    tic
    Y1 = spm_read_vols(V1);
    toc

    disp('Slice - read')
    tic
    nscan = length(V2);
    Y2 = zeros([V2(1).dim nscan]);
    dim12 = V2(1).dim(1:2);
    for z = 1:V2(1).dim(3)
        for i = 1:nscan
            Y2(:,:,z,i) = spm_slice_vol(V2(i),spm_matrix([0 0 z]),dim12,0);
        end
    end
    toc


    disp('Vol - read and write')
    tic
    Y1 = spm_read_vols(V1);
    for i = 1:nscan
        spm_write_vol(V1(i),Y1(:,:,:,i));
    end
    toc

    disp('Slice - read and write')
    tic
    nscan = length(V2);
    Y2 = zeros([V2(1).dim nscan]);
    dim12 = V2(1).dim(1:2);
    for z = 1:V2(1).dim(3)
        for i = 1:nscan
            Y2(:,:,z,i) = spm_slice_vol(V2(i),spm_matrix([0 0 z]),dim12,0);
        end
        for i = 1:nscan
            spm_write_plane(V2(i),Y2(:,:,z,i),z);
        end
    end
    toc
end