High-Speed Mode is a communication mode which can use WiMAX 2+, and High-Speed Plus Area Mode is a communication mode which can use WiMAX 2+ and the au 4G LTE which is widely available. 

Also, LTE Option is an optional service which allows you to use LTE by setting the High-Speed Plus Area Mode.

* High-Speed Plus Area Mode may not be available depending on the device model you use. 
* You can use the High-Speed Plus Area Mode by switching the communication mode on the home screen of your supported device.