you sure? because most of the 'truely unlimited data' for any carrier have tiny fine print at the bottom of their ads, saying '4G speeds gauranteed to 2GB' or somesuch. they might not technically 'throttle' you but you will be dropped to much-slower 3G or EDGE rates. there is really no such thing as unlimited data with gauranteed 4G LTE rates. not unless you have a capped data plan with tons of data allowance.
Also, you're a bit incorrect either way. according to this link, there is a mention that after 5GB you get dropped to slower speeds on T-Mobile
Does TMobile Throttle Unlimited Data? - Android Forums at AndroidCentral.com
With my Verizon data being the only internet connection available to me where i choose to live, and the amount of video streaming and large downloads i make, i would rather have 20GB of 4G LTE rates than a mere 5GB with dial-up rates slowly following that.