I was under the impression that Tyres with a larger rolling radius gave a truer reading Speedo wise. A few members on here (Aquazi for one) commented their Speedo was closer to the Sat Nav reading with 225/40/18.
205/40/17's are too small, the many disadvantages outweigh the increase in 0-60.
215/40/17 give a slight increase in acceleration and more protection from kerbing, but drawbacks are a harsher ride and a slightly bigger gap between Tyre and Arch compared to stock.
205/45/17 are the stock Tyre size for a gen 7.
215/45/17 will fill the Arches slightly better, give more Rim protection and a better ride. Downside is, as the rolling radius is increased over stock, acceleration will be slightly affected.
After trying the bottom three on my 140, I settled on 215/40 front..215/45 rear.