Sounds great until the client realises they can hire someone else who does charge by the hour, saving them a massive 100k - 10k = 90k compared to your proposition.
Yeah, your ability to charge more scales with your proven ability to deliver. That's where referrals/portfolios/testimonials/case studies come in.
Basically, you want to charge a percentage of the value you're promising to provide for them. And then that's going to get multiplied by their confidence in you.
If I'm bidding on a project that I think can make $1MM/yr for my client, and I normally charge 10% of the first year's worth of value, then I'm looking at $100K. If the business I'm working with only has a 50% confidence that I'm a safe bet to produce that value, or an 80% confidence, that's going to get reflected in what price we negotiate to. Probably more like $50k in the 50% confidence bucket.
But the more proven you are, the more you can say, "I said this thing would make $2MM and by gum it actually made $5MM" the more you're going to be able to charge.
N.B. That 50% isn't "It's a coin toss whether or not they'll complete the project", it's more like "When they complete the project, we're confident that we're going to get at least 50% of the value they're selling us on"
Really depends on the client and your reputation though, you can definitely pull it off with the right pitch to the right people at the right time.