do demos accurately show how a game runs on your computer?

So there's this game that I want, My proccesor is .4 ghz below the minimum requirements but the demo works just fine.

If the demo runs on your computer and you're happy with the framerate, graphics quality, etc. then the full game should work just fine.

I have had one occurence where I had a game, it got to scratched and stopped working, bought the updated version of it, and it didn't work on my computer. But if the demo works at a good quality, then the full game should run fine. Just see how high you can make the quality of the game on the demo, before you buy the actual game.

they should, but bear in mind that some scenarios/areas of the game may be more taxing than others. LoG-Sacrament

oh yeah, true. Like if it's an FPS you might come across a huge setpiece or something that drags the framerate down. But... .4ghz isn't that much of a difference, so I'd go ahead and take the chance anyway.