Then IB just lets me withdraw $400k in cash and starts charging me margin interest. In theory I could sell $400k of stock, withdraw the money, then buy back the same $400k of stock "on margin". I assume I don't have to do this as far as IB is concerned - but may have to do it for IRS tracing...
I'm looking to build a new home and don't want to sell stock to do it. Interactive Brokers (IB) margin rates are 1.57% on the first $100k and 1.07% on the next $900k. I currently pay 2.875% on my mortgage and would expect to pay more on a new loan in particular if it was a construction loan...