First the "box speed" of any film is the ISO rating, D3200 has a box rating of 1000. Delta 3200 is just its name.

Second shooting TMax 400 at 1000 in my world is "inside the limits". I'd shoot there and develop normally without a second thought. You should test that all the way to the print to see if it works for you. Same for D3200.

My bet would be that you find TMax 400 less grainy and D3200 more grainy and that both are beautiful.