IMHO, I don't think a cabinet with drawn air will keep anything cooler unless you have the ability to do a flow study and testing to get proper flow through the entire cabinet. A couple of small fans aren't going to be sufficient to adequately vent a large rack. Heat rises, so it will naturally vent itself; just having enough open space and enough room for the air to move on its own could be enough if it isn't a lot of gear or a lot of gear that generates a lot of heat.
An open rack doesn't really need to take flow into consideration because the heat is directly transferred out in whatever direction it likes.