In my experience you'll be much better off just quitting and joining other companies, then going onto contracting.

Here's my own person experience in just a few years:

1. Start off as a Grad on 30k GBP

2. One and half years later quit, onto another company at 48k GBP (>50% pay rise)

3. One and half years later quit. Do own thing for a year. Then go onto contracting at equivalent of 75k GBP (>50% pay rise)

So in summary, in the span of a 4 year period, I've gone from 30k GBP to 75k GBP.

There's definitely an upper limit on this of course. I think if I were to get out of startup land again now and focus on my salary I'd have to head to a different market (currently in Australia). I'd either aim for contracting in the UK where I know you can easily get 400-600 GBP per day, or the US where salaries for devs just seem higher.

I'm playing long game though, taking the startup route. So I'll either be collecting change from the streets in a few years, or hopefully I'll be well ahead of the game. Will have to wait and see...