Normally by just increasing the R of your wheels you must expect some (not too big) loss in acceleration and also some small gain in top speed. On the other hand increasing also the size of tyre lets say from 185 to 205 width for the R17 wheels then u will also loose something due to increased friction.
On the other hand you must have better handling (not in wet road though).
My personal opinion is that the R17 wheels are a bit too much for the car's power, (a R16 would be maybe better), but I also like them very much for the looks (also ordered the 1.4 16v Sporting GP)....therefore, I would say....go for it....
The lowering of the car (not much) will also improve the looks and handling but may become a bit bumpy.....
Good luck....