I'm not sure it would matter that much TBH. In your case, what you could do easily is flip the rear exhaust to an intake and leave the others alone. That way you still exhaust warm air out the top, but you have fresh air coming in to your CPU, and you have positive pressure instead of negative.
Well now... I never thought of that. Thanks @Bartacus ! That would be an easier change to try. Flipping that back fan is easier to get at than trying to flip the top ones.