Help ! Best MC cartridge for Linn LP12?

Well, the Kandid would be the logical choice . You did not mention which phono pre you are using? If you already have the Radikal, the Urika would provide you with a fully integrated SE deck. The synergy with the Urika and the Kandid allows them to punch way above their price point,imo.
I run two LP12's similar to your spec however with Naim Aro arms. One deck has the Kandid/Urika and the other has a DV Xv1-s/Whest Titan Pro. They both are very engaging and musical.
There are some other things to consider before spending 10K on a new cartridge imo- PM me if you are interested in a dialogue ...
ATB,
Mark

Dynavector, Lyra, Transfig all work well on the Ekos ...It's a matter of what signature sound you are looking for. I am a firm believer in spending the $$ on a great phono stage and a great interconnect rather than on a cartridge which wears out. 
As you are a Skale user, I recommend you look into Tiger Paw's Tranquility- very significant upgrade for relatively small investment. As with all things LP12, a good technician is paramount to set up the deck properly. Seek one out if you are not very familiar with how the LP12 is assembled- this will make the biggest difference,imo.
The Tranquility is not a subtle change....
A really good interconnect from your phono pre to your preamp will also make a huge difference at the level of your deck- I use Chord Music and have been very happy with how little they do :)
ATB,
Mark