Maximum PC

Moving soon to a MORE rural area--no cable or DSL available, but there's a local fixed wireless provider. They offer five service level plans--"sustained data rates" of 512Kbps, 768Kbps, 1Mbps, 2Mbps and 4Mbps and corresponding "burst up to" rates of 2Mbps, 4Mbps, 5Mbps, 7Mbps and 9+Mbps. I'm not sure how to compare these rates to the cable service we currently have in town. We can get a max of 3Mbps on a speed test from a server 80 miles away. On downloads, I've never seen a speed faster than 275-300Kbps. That's adequate for our current uses, but of course faster is always nice--and our uses may change. So, what figures do I use to compare to our current service--sustained data rate or burst rate? Is the 4Mbps sustained data rate fast enough to stream HD movies from the internet?

I'd appreciate any help or comments. Thanks.