I use a 304 for my TV server. I have had no problems with heat building up inside the case. There are 4 mechanical drives and 2 SSDs, a 3570k with the stock heatsink using the out of box fans on the slowest settings. It transcodes and streams video 24/7.
acpitz-virtual-0Adapter: Virtual devicetemp1: +27.8°C (crit = +106.0°C)temp2: +29.8°C (crit = +106.0°C)coretemp-isa-0000Adapter: ISA adapterPhysical id 0: +64.0°C (high = +85.0°C, crit = +105.0°C)Core 0: +58.0°C (high = +85.0°C, crit = +105.0°C)Core 1: +64.0°C (high = +85.0°C, crit = +105.0°C)Core 2: +64.0°C (high = +85.0°C, crit = +105.0°C)Core 3: +52.0°C (high = +85.0°C, crit = +105.0°C)