My wall may not be the same as your wall -  the sensor size is the same and the number of light receptors is more on one than the other but I like to deal with something I can hold in my hand and that is a print.
A print made from the 400D printed at the same resolution as a print made from the 350D would be larger.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html