Using both LR35 and LR4B, it is possible to change the size of grid photos from the Library view but whilst using the second monitor in Develop to view the grid, all of the images are displayed with a fixed size.
Or at least I can't work out how to change the size of the images in the Develop grid.
It would be nice if a "grid was a grid" and that all grids behaved and were controlled in the same fashion.