Help ! Best MC cartridge for Linn LP12?

glennewdick, the system that you heard the 'fully decked' out LP12 is an interesting one....please do tell us what the 'fully decked' out LP12 consisted of? Hate to stir the pot here also, but I think one could safely say that a Quad 57 system driven by 6 Quad mono amps would be in of itself a little.... colored. I like the sound of the 57's--a lot, but the Quad mono amps were not the most 'resolving' IMHO, LOL.

Everyone, the suggestions are excellent. To address some specifically:
1. Vibration/ footfall- a HUGE problem I discussed in previous posting. Resolved by ripping out floor under equipment & pouring 12'x 8' x 5 deep concrete slab. Ran separate dedicated 20a supply circuits with 8' deep copper ground. Equip rack is Critical Mass Soto  Vocce w black diamond iso shelves. Noise floor & vibrations pretty well handled now. 
2. All cabling is Transparent Reference or RefXL. The AQ Leopard TA cable is stiffer than the Linn cable, but I was careful to install to allow movement. The SQ improved so much I'm not going back to the original.  
3. Great point about upgrading phono section over cartridge w limited life. In fact I can easily audition a few phono sections in my price range to see if I get the improvements I'm hoping for. I want more resolution or detail than I currently have, particularly in the upper midrange. Maybe even more analytical, if I could actually hear an example of what that is. I'd like a little more extension in the highs. Of course everyone wants lower noise floor, speed & broader soundstage. 
4. Having hybrid system with a full lush sound now, going to a SS phono stage might be a option. Any thoughts on Merrill Jens, T+A, vs
Lamm, Zesto or Aesthetix Rhea ? This change might as impactful as going to a Lyra Etna or DV1-S, which are my first choices for a cartridge upgrade.

I honestly appreciate you the helpful and thought provoking responses. For the other responses, go f yourself. Haha. 

To be honest I don't have a list of everything that was done to the LP12 but I was told by the owner it was pretty much maxed out for upgrades. the rest of my  friends system is  Nagra PL L pre amp. driving the 6 Quad mono blocks all have been fully upgraded and rebuilt removing the silly quad cabling system. The work was done by a local friend who builds $25k SET amps and the quads sound very good indeed. the Panels have all be rebuilt and are inside a custom bamboo frame one on top of the other. the whole system is in a dedicated audio room built specifically built for his system with a sub floor for isolation and wiring. I have to say his system is very transparent, very wide and deep sound stage ( best I've ever heard) and fill that room totally. even the base is great with 6 panels. i'll add a couple pictures I took of his place to me profile if you care to look, he's got 15000 records on the walls lol that's what blows me away lol. anyway i'm not saying the LP12 wasn't good sounding just not up to what the others had to offer in musicality drive and toe taping pleasure.