Thanks to all for posting..

Upshot seems to be that 215/40/17 fit without problems even though the 205/40/17 is a closer match to the original 205/50/15.

I should have said from the off that the car is lowered (about 25mm i think), and the wheelarches haven't been rolled (and i don't want them rolled)... bearing that in mind, 215/40/17 still the size to go for?