Go find the original data from the Magellan Probe. From this you can get the temperature and pressure at various elevations on Venus. From that you can get the temperature at each pressure. Compare the temperatures on venus to the temperatures on earth at equivalent pressure. The relationship between the two is exactly proportional to the square root of planet's relative distances from the sun, exactly as predicted by the inverse square law and stefan-boltzman law. There is no room for greenhouse effect in explaining this data as far as I can tell.
Is that above or below the clouds? (Below the clouds there should be little greenhouse effect anyway, methinks, since little light gets down there. And above the clouds the shorter wavelengths should be refleted off to space without conversion to infrared, so I would expect no greenhouse effect either.)
It works for Earth troposphere pressures (200-1000 mbar) which overlaps the cloud layer. It is slightly off within the cloud layer. Anyway you seem to be proposing an alternative reason there is no affect of CO2 on venus's temperature, and thus no evidence for runaway greenhouse effect.