Prominent Backers

That number is sure to rise, since better-quality borrowers have no logical reason to stay put and subsidize others, said Vince Passione, founder of Lendkey Technologies Inc., which connects students online with private student-loan lenders. In April, an affiliate of Apollo Global Management LLC, billionaire Leon Black’s private-equity investment shop, said it plans to invest $1 billion in refinanced student loans through LendKey.

Other big names are taking notice. A company called Earnest, which started online student-loan refinancing in January, has backing from Silicon Valley venture-capital firm Andreessen Horowitz, famed for helping seed Facebook Inc. SoFi’s investors include another hedge-fund billionaire, Dan Loeb, and Peter Thiel, a co-founder of PayPal.

New York-based CommonBond Inc. -- founded by three classmates from the University of Pennsylvania’s Wharton business school -- rewards borrowers with dinners at popular spots such as Grafton Street, an upscale pub near Harvard in Cambridge, Massachusetts. It also offers $200 for referrals.

$140,000 Income

The average CommonBond borrower is a 32-year-old who makes $140,000 annually and has a near-perfect credit score of more than 760, said 34-year-old CEO David Klein. He took a break from Wharton three years ago to start the company, backed by education-finance company Nelnet Inc. and Vikram Pandit, Citigroup Inc.’s former chief executive.

Even for strong borrowers, there are risks to forsaking federal loans, which feature reduced payments for borrowers who get sick or lose their jobs, according to Rohit Chopra, the U.S. Consumer Financial Protection Bureau’s student-loan ombudsman.

“They should be aware of what benefits they’re trading away to get that lower payment,” Chopra said. The loans -- such as the one to Winiarz, the California money manager -- can be variable and reset monthly, exposing borrowers to the danger of a sharp spike if the economy shifts

For now, taxpayers will be funding a greater share of borrowers like Noelle Liptak, who lives near Akron, Ohio, and makes $40,000 a year as a marketing representative for a plastic-bottle manufacturer.

Liptak, 31, has almost $100,000 in federal student loans from college and an MBA from Point Park University in Pittsburgh. A government program currently lets her pay $46 a month, and her loans may be forgiven after 25 years.