So with my new wheels I decided to drop the front slightly with some new springs. I did some reading and decided King Lows (KCFL-42) with a 45mm drop were the go. I put them on myself and it didn't seem to drop much - but I expected with some driving around they'd sink/settle a bit. A few weeks on now, and they might have dropped a little, but not much.
Then I read somewhere that the Sports already had low springs! DOH! Is this true? Have I just wasted my time and money replacing low... with low?

Sports is less the low SP at about 10 to 15mm drop from factory. No where near 45mm drop. What are you measuring to determine drop?
You should have measured distance from the centre of the wheel to the top of the wheel arch before fitting the new springs and after. This measurement is not affected by wheel/tyre size changes and tyre pressure changes.

The 45mm I'm talking about is the quoted drop for King Lows (unless I'm mistaken?) I haven't measured anything myself, just going on appearance it seems to be roughly where it was before I swapped the springs. Anyway, if the Sports was only 10-15mm drop from standard then I'm happy I haven't wasted my time/money. Cheers.