That shader 3.0 thingy only helps ATI cards in the clouds, the Nvidia guys won't see any fps improvements.
The 'zoom out haze' is a known downside there, but all water related things can be tuned when sticking to the included readme.
You are just seeing Bojote's preset there, which can be altered.

But I would recommend reverting back if the optics didn't improve for you. As said, the FSX clouds come with the general downside of causing a large fps impact when using any type of super-sampling anti-aliasing. So I would, for testing, recommend to go to a normal AA mode and see if that help the fps. It should, be design.
Use the driver menu or tools like Nvidia Inspector there and avoid any SS (which stands for super sampling) in the mode descriptions.
Also, any transparency AA (which uses super sampling) will put more load on the card, so maybe leave it off for testing.
You can later apply some more AA until reaching a point where the image quality doesn't improve much more while the fps stay friendly. This will always be a tradeoff situation in FSX.

The modes you can use (with clouds) depend on your card. The smaller ones struggle some more while you gain some headroom on the top models. But even a GTX580 can easily be spoiled with the combination of SSAA and dense clouds, don't get that wrong. The way that FSX draws clouds is the culprit there.