The Quake Retexturing Project optimal resolution set is better graphics-wise and are higher resolution than the unofficial installer I built.
I focus on the effective rendering quality and on file size. I want everything to basically look just as good, but be a smaller download.
Here are 2 examples in JoeQuake 640 x 480 resolution.
6 MB Installer Vs. ID Software Originals
The different in the above is obvious. The ID Software originals don't match up the Quake Retexturing Project textures from the 6 MB installer. The QRP textures are a LOT crisper.
6 MB Installer Vs. Quake Retex Max Resolution
This comparision isn't versus the QRP Optimal Set, it's against the QRP Max resolution set. If you increase the resolution to a higher one like 1024 x 768 or 1280 x 960 and then look at the floor, it's going to be a lot easier to tell the difference.
It is very difficult to casually tell the difference. Now the above is 640 x 480 resolution, which is what I use.
One reason why it is difficult to tell the difference is that Quake is 3D and unless you are standing right next to the wall, you are several Quake feet away from any given wall.
It is my understanding that Quake works by making 4 scales of MIPS --- think of them as decreasingly small textures --- from the originals. Which may be a major reason it is so difficult to tell the difference unless you are carefully examining.