Did you have the top fans in intake or exhaust configuration????Using them as intake will create positive pressure,thus limiting dust...Another idea is to use them as exhaust and reconfigure your push/pull configuration to intake.So,you'll have the three intake fans delivering fresh air to your gpu/hardware,fresh air coming in from the cooler fans,(instead of pulling the hot air coming from your 780 classified),and the top fans exhausting the air out of your case..But then again,if you probably tried that,since you didn't notice any temp improvement,it all comes down to the level of noise you're comfortable with coming from your pc.I,myself,would not cover them in the end,because every chassis is designed by the manufacturer to have a standard airflow,and that might mess it up IMHO....