Something that helped the airflow greatly in my T320 (upgraded with T420 motherboard) was replacing the factory heatsinks with dual Noctua NH-D9DX i4 3U CPU coolers that have their own individual fans, and then replaced the factory exhaust fan with a Noctua NF-12 iPPC 3000 PWM. I also added a Noctua NF-A14 fan into the upper area above SAS drives to blow at the upper PCIe area at the rear. This configuration allowed me to manually control the rear exhaust fan and lower the speed down to 40%, which is very quiet with the new Noctua fan.

With the row of Noctua CPU fans creating an efficient breezeway under the shroud and the now slower (and quieter) exhaust fan evacuating that heat, the system is near silent and the CPU temperatures never get hot even under heavy stress testing. This is with dual E5-2470v2 processors. This efficient flow of air under the shroud also creates a hefty suction at the front lower SAS drive array.