I'm on Comcast's 30mbps tier, and as of Dec 31, their monthly usage meter indicates I've used 153GB of the 250GB they alot (Though the cap is temporarily suspended). And we stream daily for at least 2 hours-more on the weekends, not all of it HD ...
So the 250GB cap should suit your usage patterns without problems.
Sigh...the whole point of getting broadband, was to free you to do the things you wanted to do. Now after everyone's hooked, they want to shove us back to a shoebox. It's just 2 in the house for me, but I do feel sorry for households with kids or online gamers who may get pinched by these caps.
Dazed and confused over high tech.
Sigh...Concrap. The Internet Overlord Cometh
They're not com-tastic!