For info about the Zantec cases, and this may also apply to many others with both top and rear vents. I played around with temperature probes and fan contollers quite a bit and I found that, if you run just a rear fan as an exhaust, then most of the air is drawn in through the top vents (hardly anything through the front or bottom) and you get very little circulation through the case. Likewise, if you use just a top fan, most of the air is drawn in through the rear vents and you get very little internal cooling. Initially, I used just a rear fan and taped up all the vents in the top of the case. That worked well and drew most of the incoming air through the front (over the HDDs) and the bottom giving much better cooling of all the internals. The downside was that I lost the passive cooling effect of warm air simply escaping through the top vents and the fan needed to run more often. My final strategy was to use both a rear and a single top fan connected together to one channel of my fan controller. So, I still get passive cooling and at "idle" none of the case fans run at all. When I'm streaming or otherwise using the server and the temperature rises, both fans come on (slowly at first) and draw air in through the front (over the HDDS) and the base.
