I have owned both. I had a 1.4TSI FR 5 Door for 6 months and now I have a 1.8TSI SC FR. In all honesty, the power difference is hardly noticeable, especially in round town driving (the 1.4 felt more powerful in this situation).
The power of the 1.8TSI is only noticeable at higher speeds in high revs.
The MPG is almost identical, but then I can only achieve 35mpg tops in either based on the way I drive.
Hope that helps