MBS are shooting up nicely today.  Lenders won't price all the gains into their sheets until the gains hold for a bit.  Nonetheless we might see some very aggressive reprices very soon.  Given the volatility of the market, although my general sentiment leans towards floating, you might benefit from doing the same thing that some MBS holders will soon be holding: take the money and run.

Usually when we shoot up like this "profit-takers" step in and the curve comes back down again.  So even though there is more upside potential given market conditions, there tends to be some technical resistance to much higher gains than we have now. We're just now touching the ceiling of bond prices set at the end of February.   All in all, I still recommend floating, but recognize the possibility for a rapid turn around today or tomorrow and be ready to act accordingly.