A SEP is indeed better.
If you are a sole proprietor or LLC, you can sock away 25% of your after-employment taxes (FICA, Medicare), and you only hit a cap if you're making over $200K/yr
If you have an S-Corp, the Corp can put 25% of your salary, pre-tax into the SEP. So you take whatever amount you billed this year, divide by 5. 4 parts become salary, the 5th part becomes your IRA contribution. It adds up fast. Then again, having the discipline to save 20% of your income adds up fast no matter what you do with it.
I can only speak from my personal experience, but I have no idea where the 60% figure was sourced. I live in NYC and it's more like 40%, and income tax rates follow the same graduated scale that a regular employee would have.