The Fed can cut rates to zero, even theoretically below zero. Lenders cannot. They must be profitable and hedge against inflation. If cost of funds is zero, and inflation is 2%, the cost of servicing and originating would push fixed rates to 3.0%, but doubtful to see 3.0% at "no cost/no fee". ARM loans also won't see zero percent given that most Margin Floors are 2.25%. There are a few "zero margin" 1 month LIBOR loans, but to qualify for these loans require near god-like financial strength. Who wants a monthly ARM today anyhow? Could you sleep at night with one of those things? Not me.
One differential is the movement of funds. For the fortunate few among readers here, if a 3.x rate comes along, and you can move money to a bank for a rate discount, that action has the potential to reach 3 or even sub 3% on a 30 year fixed loan. If you don't have the cash to move, it's "no soup for you"! unfortunately until the market really falls over.
When I worked for a bank that used a wild west mode of transportation as their logo, they offered a 2% below Prime rate HELOC to their best clients. At the time however (2005-2006ish) pretty much anyone who could fog a mirror was a "best client".... but I digress. Some of these HELOC's saw a 1.5 rate during the 2008 financial crisis, a pretty great deal for the customer. Not so much for the Bank. Since that time, most super banks have (for now....) learned their lessons and put floor rates on their products.
Bottom line, sub 3.25% 30 year rates. sub 2.875 15 year loans and sub 2.5 fixed period ARM loans are a solid "buy of a lifetime". If you can get them with minimal or no cost, the time is now to get it done.
My .02c
SGIP