With this would it be possible to do a full screen mode on the upper screen?
It's not possible to do full image stretching AT ALL (due to the matrix hardware only having 8 steps max, and a full stretching would require 25/12 division) and partial stretching requires extensive patching (albeit doable, and exactly 2x on the X axis due to 24/12 fitting into the matrix hardware's range because it can be simplified to 8/4).
On the other hand, if I understood correctly: when using this patch x1.25, which is the same original size, applying it removes the blurring effect and weird color that comes in stock?
It does correct some color problems caused by the original awful matrix, but the color will be mostly the same.
As for the blurriness, the manual patch removes most of it, except there is a grid-like pattern of blurring in it to make it just ever so slightly less an eyesore due to the 5/4 upscaling ratio.