Query on Discrete Cosine Transform(DCT)

Question

Hello,

I am doing some basic Matlab simulations on DCT used in Video Compression. I have following questions arised out of that:

1.) In a 16x16 MB , if one does a 8x8 size block DCT (4-times) for that MB in first case and a one shot 16x16 size block DCT in second case, Will the reconstructed block at the decoder will have same/similar values in both cases?

2.) Which case would there be any benefit in terms of lesser residue, lesser bits needed for coding etc?

3.) Will this analysis of block DCT also hold true for other transform like the integer transform used in H.264 codec?

Regards -Ajit