max. frames ahead means the amount of frames that are rendered ahead, when you disable vsync. (synchronisation between the frames outputted by you videocard and the refreshrate of your monitor. enabling vsync should reduce the 'tearing effect' some people experience, but it will however limit your fps to the monitor's refresh rate. bad for benchmark purposes) I guess it's just fine leaving it at 3 frames, as I never noticed any performance increase by setting it higher.
digital vibrance will increase the color-intensity (as you might have already noticed by moving the slider to the right) and therefor providing a more vivid image. I love it in games such as Morrowind, FarCry or Pro Evolution Soccer, as the more intense colors look great on grass // landscapes.
check the following image out for what I'm talking about
:
without Digital Vibrance / with Digital Vibrance
There won't be any performance loss by enabling this feature, so you just might experiment with the slider to see which profile suits you best.