The center fan on either of those towers does all the work. It's draw is through the front heatsink, it's exhaust is through the rear heatsink. Both those towers can also mount a fan in front and rear, so possibly 3x fans total. In the big scheme of things, the additional fans don't do all that much work, their only real job is to direct air to/from the center fan, streamlining efficiency. This will lower temps on the cpu, at the expense of bleed across the motherboard. Is that worth the extra few °C? Not really. A cpu could honestly care less if it's running 45°C or 65°C. That's only relevant to benchmark chasers or idiots who believe that cpus need to be as cold running as possible, bragging rights.