Weird Fluctuating Performance with FSX

[Thud]

With my old graphics card I got like 3 fps at the highest settings and now with my new card I can get about 12.

UNLESS...If I set the graphics WAY low, then crank 'em up, I can get about 20-25 fps at FULL settings!

But while they're set as low as possible, I get like 50fps!

When I first bought the card, I got like 60fps with dense autogen, and middle terrain settings, full water, not many clouds. But then the next day, same settings like 30 fps.
And then sometimes I have 1/4th the settings for terrain dense/normal autogen and not many clouds and get 12fps!

So why does my performance fluctuate so much?

[Boikat]

There are so many variables, it's hard to say. If you are flying around cities and have ground traffic all the way up, the size of the city will effect frame rates because there's more ground traffic, more buildings, and more air traffic, for example.  Also, if you are flying real world weather, that could be causing a variation.  At least, that seems to be what causes variable frame rate drops for me, so I run with low ground traffic, and medium GA and commercial, and usually, "Clear Skies", or "Fair Weather", unless I'm flying in low population areas, then I like to fly real world weather.

Weather wise, you might try "simple clouds" unless you already are.