A while back I won a Sigma 20mm f1.4, which is just perfect for my uses. Unfortunately it doesn't come in K mount. Sigma offered me instead any other lens up to the price. £600 or so. haven't taken up the offer yet and I might be able to choose a more expensive lens paying the cash difference (although I haven't asked).
Are there other lenses I should consider?
I already have the 3 Ltds and the Pentax 100 macro is good enough.