Tywyll said:
Here is my question about the Immortal Guidebook, and I admit that this might have been answered somewhere else, but with 30+ pages of posts, I will never find it. 
How do you deal with the disparity between characters and creatures modierfiers to hit and saves at extreme levels? I have run some high level stuff, both epic and my normal year and a half campaign hitting the 15-18 area. The issue I found was the monsters and characters became extremely focused. This was because the random element, the d20, only had 20 potential results. So I had the issue where monsters either could never hit, but their special abilities might be useful, or in order to hit, no one could make the saves versus their special abilities. In a group we were playing around with recently (25th level) its almost impossible to find creatures that are challenging without completely hosing other characters in the group. Its almost all or nothing.
How will your material handle what is, to me, a fundemental flaw of high level gaming?
I can answer this. Due to the nature of the CR/EL relationship, creatures within the PCs' CR/EL range should fit pretty well with the level of challenge that should be represented.
Please note, however, and this is from me, that at high levels, you have three specific things you MUST simply live with:
1) PCs and creatures that are supposed to be in melee will probably always hit with almost no exceptions.
2) Saving throws stay pretty even, but more often than not, saves will likely be easy to make for both PCs and creatures.
3) In high-level games, battles boil down to who lasts the longest (like in a video game RPG) and drift away from the issue of who may hit first or fail a save first.
Also, please note that while an EL+4 is a 50/50 challenge at lower levels, it may favor monsters at higher levels, depending on the equipment of PCs. Things should not vary too much, however. As long as you remember the above three precepts, you should be okay. There is no mechanical way to keep the "randomness" in the game using the d20 because eventually stats will override almost every single roll made. Thankfully, as the DM, you are able to create monsters/NPCs that have suitable stats for every encounter. Even the ELH states that the randomness should disappear at epic levels, replace solely by DM discretion. There simply is no way to stop this no matter what system you use.
Anyway, I think that should answer your question.