Regarding desired features, I was going to make a joke about the name of the big fan on top, but I'm not sure it would be appropriate on an open to all ages forum.
That being said, if that front fan is one of their AP types, AFAIK they have higher static pressure than typical fans, and combined with the positive pressure design, should be able to push air through the HDD cage OK. Positive pressure doesn't just help avoid dust sucking in, it assures the interior air is forced out where it should go. There's more chance of each fan doing it's job properly in cases with slight positive pressure, than in thiose with negative pressure.
As for the top being used as intake or exhaust, I would first select a good side fan, then add it's CFM to that of the front, and see if it is equal or greater than that of the top, rear, and PSU fan. Chances are unless you get a very high CFM side fan it won't be. That means if you turn the top fan around you'll have negative vs positive air pressure, which can suck dust in through any small non filtered openings.
What was said about forced airflow vs hot air rising is true, all the more so in a mid vs full tower design. Also many cases including the 800D end up with the top fans being used as intakes, and it's full tower. On a side note, although Rodney doesn't mention it in his review, the top fan is also filtered.
Overall I think you're far too worried about the direction of the top fan. To get anywhere near equal airflow you'd have to as I said get a very high CFM side fan, and even replace the front with a higher CFM unit and run them on high just to avoid it being somewhat negative in air pressure. That would result in a rather loud case for what is fairly mild use compared to an enthusiast gaming rig. As is it's pretty quiet too.
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