Questions on loan financial terms and rates

[Sukhoi]

I've put in for a couple of private student loans and I'm trying to figure out which is cheapest.

One is prime + 0.375%. Another has a margin of 4.65. I don't see any other financial numbers on that promissary note other than the loan origination fee. What's the margin? How do I tell which of these is actually cheaper?

 

[Sukhoi]

Ok, I've figured out the margin part. Actual rate is the LIBOR plus that 4.65% margin.

Now, how are the LIBOR and Prime Rate related? What is the historical performance difference? Is the difference constant?