After some testing yesterday, the need for heat sinks seems to vary from ship to ship. My combat Python gets hot when deploying a 6A SCB, but if I don't use a heat sink it only causes about 2% module damage when it hits about 150% on the heat meter. But... I don't want to give up too many external slots to heat sinks. So.... after I've used the 4 charges in the one heat sink that I carry, I just use any additional SCB's needed and take the heat damage. The repair costs have been minimal so far, but I've only not used a heat sink with a 6A SCB a few times. I think that a 5A SCB in a Python wouldn't require a heat sink at all.
My new FDL seems to run very cool (besides looking and sounding cool as hell!

) and doesn't even get up to 100% on the heat gauge when I fire a 4A SCB. No heat sinks required on that ship, IMO.
I haven't tried the SCB's on the Asp yet to check for heat.