For credit card spend QF & KF are identical in points required for business class flights to Europe (and that is using standard awards on SQ, which have very good availablity, not to mention full access for A380's/77Ws), and you will need 255,000 miles and on QF you need 256,000 miles return.

Where it gets complicated is when flying - QF have higher status bonuses and minimum points guarantees that make it easier to earn points, but availability is much lower for business class than SQ standard awards. But whilst you can get 744s & 773s, or if SQ were ever to open up saver inventory on 380s/77Ws then it would require less flying than on QF.

BTW you mention 110k/220K from SIN to FRA return - don't forget the 15% online booking discount!