Sorry, I meant to say positive internal air pressure. Anyway the opposite of positive internal air pressure is negative internal air pressure. A few definitions:
positive internal air pressure is where there is more air going into the case than going out. So if you picture blowing air into a balloon and then using a needle, you poke a tiny hole, you can pretty much ensure that as long as you keep blowing, the balloon will almost always be "full" because air can't leave faster than you can blow in. In the form of a case, when the case is full with air and more is blown in, air will naturally sip through whatever tiny hole it can fine. This prevent dust build up because air is constantly moving around in the case, or more like air is so packed into it that dust is hard to gather in one place. Also, if you dust filtered all intake fans, there should be no dust in the case because any other tiny hole is blocked with air leaving the case so dust can't possibly enter there.
negative internal air pressure is where there is more air leaving the case than going in. In the same situation with the balloon, if before you start blowing air in, I use a knife and cut out a hole, you'll find it hard to keep the balloon filled. So because your case is devoid of air because all of it is leaving the case, equilibrium comes into place. Air will naturally come in from any hole without an intake fan to replace the air that left. This is tough because you can't dust filter those tiny slots. With negative internal air pressure, air is always being used so you won't have a mountain of air stuffed inside.
So no, your computer won't overheat easily or harder with either method. As you may or may not know, air is a terrible conductor. If it were a good conductor, your bowl of soup will be cold really fast. So even if you have a lot of air, it won't make your case much hotter since hot air rises and leaves the case. And since air is a terrible conductor, it doesn't draw heat away from something well. So the most important thing is good case airflow, not how much air you can pump into the case. Pumping more air means nothing. A lot of people mistake this.
I prefer having more air inside than out. Air will naturally shuffle itself and hot air naturally rises so I don't have to worry about having an oven in there. I like it to be dust free.