My guess is that salary is mostly unrelated to one's skills. It mostly depends on what company you work for, and your negotiation skills. Actual knowledge and skills are
maybe on the third place. There is also timing: if you join when the company desperately needs another developer, you may get better deal than the developers who are already there. Also, whom you know, who recommends you.
I know a guy who is 10x smarter than me, but is paid 1/2 of what I am. It's because he works at a different company. (I used to work there, too, and then my salary was 1/2 of what it is now. I didn't get twice as smart when I changed jobs.)
I know a gal who is 10x smarter than me, but is paid about as much as I am. It's because she works at the same company.
In my opinion, software companies are unable to tell the difference between developers. The bad ones are overpaid, the good ones are underpaid. Smart developers learn to code; smarter developers learn to network.
From this perspective, it makes sense to contact a job agency and tell them you want 2× what you have now. Chances are, there is a company where people with your skills (or worse) are paid that much. It just takes lot of luck to find that company. Call ten different job agencies, tell them that you only accept that much... and let them search the market. You may be surprised.