UPDATE
Found a lab test where it seems that if you use fans that spin >1800 RPM a 360 radiator can dissipate about 500 watts, enough for 4-5 Bitburners.

Web archive, skinneelabs site has been down for a while. http://web.archive.org/web/20101128200330im_/http://skinneelabs.com/assets/images/Radiators/Swiftech/MCR320/MCR320_HeatLoadChart.jpg