I'm not sure your calculations are correct, but the basic gist of your last post is what I was getting at.
At similar atmospheric pressure, the difference in temperature is about 60K; if you account for albedo, cloud effects and other effects, you possibly will be left with effect due to greenhouse gases alone. That remaining effect is most likely not zero.
This get's back to Ziggurat's point: a primary reason Venus' atmospheric temperature at the planet surface is so high is because of the higher atmospheric pressure.
But it seems certain that a portion of Venus' higher temperatures is due to the greenhouse effect.