Looking for a highend radio. Narrowed down to Futaba PX, Airtronics m12,
Kopropo K1.

What are the pro's and cons of these radios?

Rather than waiting for someone to type up and do your homework on these 3 radio's, why not peruse the 3 dedicated threads on these transmitters and make up your own mind?

Go down to your local track and try to get a feel of these radio. Go with the one that you feel most comfortable with.

This. You can read until your eyes bleed but actually getting some hands on time will give you alot more info.

Anything top of the line these days is a great radio and you can't really go wrong with any of them.

What about the Airtronics M-4X, you should also include it as well.

Never heard of an Airtronics M-4X. Do you mean MT-4 or MT-4S?

But that is a mid range radio, and although very good, it is not as fast and doesn't have the same physical adjustability features etc. as the high end model.

I have seen the 4PX in real and the finish is better than the M12. But the K1, to me, has the best physical quality finish and feel.

In that category, the M12 has a shamelessly cheap finish to it. I own an M12.

The MT-4 and MT-4S is even worse than the M12. Not saying they will break and won't last, just that the finish is "dissapointing".

Upgraded from a Futaba 4PL (which I hated the cheapo feeling plastic, but enjoyed it as a racing radio) to a Ko Propo EX-1 KIY because the 4PX blew past it's release date and I was tired of waiting for it. Been a lifelong Futaba guy but I'm really happy with the KO. The only downside is the receivers are super expensive, but I think the LCD menus are easier to get through, the build quality is superior to anything I've touched, and it has similar features. I was worried the modular design would lead to sloppiness where the parts fit together, but it's been solid as a rock. No slop or play, and I like the customization capability.

I've been an airtronics fan boy since they they first released the m8. The M12 is a fantastic radio system, and it has several configurations on how you would like the radio to feel as it has the drop down you can also utilize if you want a different feel.
This in my opinion is what you should go with, but I completely agree with the previous comments on that getting some stick time with each one at your local track would be the proper way to make your decision.

I use a spektrum dx3c and it seems like a good radio. My vehicles respond well to it. So much so that I'm wanting to use it on all my vehicles. I'm sure there's way better ones than what I have but it's what I'm comfortable with. I've used a traxxas TQ, Futaba 2PL and a Tactic TTX240

spectrum ! and you can get them used cheap sometimes