I don't know the answer to your question, but I wanted to note that 1080i is actually 60 images per second (it should be written as 1080i60), despite technically being encoded as 30 frames. The interlace lines represent two images in one frame, so you still get a 60fps image, and with a good deinterlacer as most TVs have, you're not really going to notice much of a difference between 60p and 60i.

Also, most 60i sources I've seen tend to stream as 30p because it's a simpler conversion from the source format, and easier to stream.

No

1080i. Always.