Clearaudo Concept vs Rega P6

You may be able to find some prior posts on this forum discussing the Concept TT vs different Rega TT's that might be helpful but probably not down to the carts that you are considering. 
 

I recently compared the P6/330/Ania to the Mofi Ultradeck with MoFi's better cartridge and the Clearaudio Concept with the Clearaudio MM cartridge (the $250 one).

I kept the Rega.  In my system, at least, it was noticeably better - quieter, less colored, more explosive and propulsive - than the others.  Part of that was due to the Ania MC cartridge digging out more detail, but having heard the Rega with the Exact2 MM cartridge, most of the difference is from the table/arm.  It's a great combination, and I wouldn't be surprised if it wouldn't be better than my old LP12/Lingo/Cirkus/Aro/Troika setup from long ago.  

That said, system matching matters - I have an Exposure 3010S2 preamp and 3010S2 monoblocks driving Monitor Audio GX300 speakers, and it's not hard to imagine a system where the Clearaudio or MoFi tables worked more synergistically, even if the Rega's margin over those two was significant.  IMO, obviously.  

I would go with the Clearaudio.  I had a Rega Planar 3 and hated it. Much too lightweight sound.  

Clearaudio Concept.

I had the Rega and then switched over to the Clearaudio Concept. Its much more robust.