Bob's right (in my experience). If analog FM Stereo is completely clean (not "blended", and fully quieted), then you should get the HD.
By the way...HD power is 1/100th of the analog signal, not 1/10th. A 100,000 watt station has a 1,000 watt HD signal. Don't worry, this is comparing apples and oranges. HD doesn't need to be received "cleanly" (free of what would be analog noise). All that's necessary is that the radio be able to tell the difference between a one and a zero. THAT requires FAR less power.