Out here in the Seattle DMA, the spotbeams seem quite wide -- definitely wider on SD than HD... for SD, even 150 miles north of Portland I get 100's on both TP's for Seattle and Portland... I even get the TP's for Sacramento and Salt Lake City on 101 with between 30-40, which would be watchable as long as there was no rain at all--and if I ever wanted to "move", I could get a bigger dish and fix that.
HD is the same situation with Seattle and Portland, plus Yakima (about 100 miles away as a crow flies) comes in around 80, and Spokane (other side of the state) comes in around 75... I think Bend/Medford is in there too since I get a couple HD spots in the 40's... SLC and Sacramento seem out of the picture HD wise (I haven't mapped the TP's for 119, but I also get a bunch of 119 spots in the 60's - 70's so it's probably Yakima/Spokane/Bend/Medford which means they would come in perfectly fine SD as well).
I know there are a few areas with "tight" spot beams in the east... but you can still watch your locals with signals down to 30-35, provided there is no rain, and they don't "overlap" the same TP's at the edge, so for the most part you can go pretty far.