Linn Basic LVX or Rega RB300 ?

Personnaly I would stay with a Linn arm. Linn has a way of working together with other Linn components. Also the Rega arm may pose some issues in spring tension setup. All just MHO of course.

Well, I ran a rewired RB300 with a Cardas Heart on an LP12 Lingo for a number of years. The tensioning spring was removed during rewiring and the VTF was set with the counterweight. There was no problem whatsoever with setup or installation, or with day-to-day operation. My Linn dealer did not recommend using the Heart in the previous arm, an Akito, which I understand is a better arm than the Basik, indeed the best MC he would go for was an AT OC9. The Heart worked really well in the RB300.

I have pics of the setup if you like.

You'll probably need to get another armboard if you want to mount the Rega. Origin Live makes a pre-cut board. I don't think that the Rega arm is much heavier than the Basik, though you'll definitely have to check the Linn's spring adjustment and be careful with the cable dressing (I'll be fitting a Tecnoarm to my LP-12 later this week).

If your P-25 is still running, it might be nice to have two TT's working.....perhaps running a different cart on each? The Basik is not a bad arm at all - but as Viridian has already stated, a bit limited in the choice of suitable carts. A Dynavector 10x5 worked well with my Basik arm. I currently have a Clearaudio Virtuoso on it which is working very nicely.

I would sell the Rega and the Basik and get an Ittok. That's the arm you want on the LP12.