I got a little confused there between where you said you would have a much lower rate, and then where you talked about a 0% BT.
As the others said, yes, it's helpful to have an installment loan in your mix, but I wouldn't open one solely to please the FICO gods by improving credit mix. If it saves you money to open it, great; otherwise, keep in mind that it's available should you need it in the future. And as marty said, if you do move any balances around, keep the original card open.
* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit?
FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007