As you can see, sharpness-wise there isn't much difference between both pics. Note that it is a 100% crop of the cantral part of both images. I took them handheld, stepping backwards between the two shots, therefore getting two equally composed pics. Notice that with the tele lens the image looks a bit brighter because of the sun shining true the clouds a bit more (notice the shadows).

I must say I was very, very, very pleased to see this result. You can't see it in this crop, but the pics look sharp even in the edges and distortion is not an issue.