T-Mobile's $30/month pre-paid and Nexus 5

Once the Nexus 5 comes out I plan on switching to that and T-Mobile's 100 minutes, unlimited text and 5 GB of 4G data plan that runs $30/month. For those of you guys who run this already: do you guys get the full 42 Mbps speed? after 5GB does it fall to 3G like other pre-paid plans or is it just that then you're out? Ease of purchasing the plan and getting on it?