3 different style.css within cc-theme

Hi Forum,
I need some advice regarding css-style-files hierarchy.
I am using an cc-theme which allows css-tweaking through theme-settings. At the same time I have established a child-theme holding same php and a couple of css notations as well.
On top of those the NextGen Gallery provides a menu to tweak the gallery style via css.
Now, my Thinkpad T61 can’t handle the css correctly and I thought it might be the fact that the css gets fed by 3 different custom css-files.
Would it be better to copy all custom css into one style.css and feed it via cc-child or cc-themesettings to the theme?
Best regards
dan_worg