Graduate Loan Arbitrage with a Bank?

My only real financial scourge in life are my school loans.  Specifically, some of my graduate school loans bother me the most because of their high interest rates.  The offending group are officially 7.9%, of which I pay them back at a 7.65% rated due to auto-debiting from my bank account but I digress.  I pay more than the minimum and all of those extra payments are directed at these higher interest loans.  In my opinion, I’m not that risky from the lending standpoint.  At least, not 7.9/7.65% risky.  I’ve made every payment on time in my life for my various credit accounts (school loans included) and keep a low debt utilization ratio.  Has anyone taken out private loans to pay down federal loans simply because the interest rates were lower and they could take advantage of it?  e.g. Did you take out a loan from a private lender at 5% and use it to pay down a 7.9% graduate school loan and essentially save 2.9% in interest payments?  Were there any unforeseen drawbacks?

For my specific situation, trading the owner of the loan wouldn’t hamper my ability to still pay down my loans since such a high proportion of my payments are extra payments.  I currently owe $482 every month buy pay, on average, about $750 in extra payments in addition to the $482.  I’m guessing if I used a private loan, a portion of the $750 extra payments would just go to the private lender rather than to Uncle Sam.

So basically, has anyone has any success with banks wagering on them for interest that otherwise Uncle Sam is collecting?

I haven’t called my bank, or any other private institution yet but wanted to get a pulse from those that have tried this path.

Thanks in advance.

Note: I’m talking about grad loans here specifically because they have the highest interest.  Obviously if I knew I could turn a 7.9% loan into a 4% loan and my non-grad loans current interest rate was higher than 4%, I would do the same with them eventually.