Here is a link to an online calculator:
http://www.torquestats.com/modified/index.php?pid=calculator
which does indeed generate figures close to that claimed by FIAT.
Of course, it also depends on how you're measuring your speed. If you use the car speedo, your figures will likely be 5-10% optimistic.
Likewise it provides a very similar figure to the one claimed for our Subaru...... http://www.carfolio.com/specifications/models/car/?car=28611