I went from good to bad to good. I had a great running FSX, but to make a long story short I had to reformat my drive and found that the backups that I thought I was doing to a terastation, really weren't getting there, so I had to reinstall FSX fresh.
I spent days doing all of the famous tweaks, and things went from horrible to unplayable. I was getting nowhere.
So, I decided to reinstall FSX again and made sure that all the folders and FSX config were gone when I did the uninstall. Then I just did the minimal amount of tweaks in the FSX menus after the install, and I'm not sure I did any in the FSX config directly, and FSX is flying better than ever.
The only other thing I did was install the latest version of DirectX (I'm using version 9). I had forgot to do that in the first reinstall and FSX had loaded version 9.0C, so the second time I loaded the latest version 9 - I don't know what it is off hand.
My question about all of this is - Does FSX use the info stored in the FSX config to configure other parts of FSX as you are starting and playing the game so that the more changes you make to FSX config makes FSX, in general, more unplayable? I can only say that I do not have the blurries anymore and I am thankful for that. The more I tried to tweak the FSX config after my first reinstall, the worse the blurries got - it was like there was a demon in there.