This way, I can do the following.
1. all cost is on the first mortgage, so the earning on the rental property can be offset by depreciation and other costs, which the mortgage is fully tax deductible.
2. Super conforming loan only exists this year, it will be gone next year, better catch it. I plan to get 30year fixed for the first mortgage to ensure that it is stable.
3. If the rate goes higher, I am doing ok since I locked a low 30 year fixed first mortgage.
4. If rate goes further down, I am OK too, since I have $250K loan floating in equity line.
I think that it is a balanced strategy and relatively safe. I highly recommend this.