PHY data rates for any HAN technology, except good old Ethernet, are lies, but they are useful to compare within technologies.
G.hn has been claiming they are 1Gbps, but DS2 told a local on-line magazine that their next G.hn chip is only 400Mbps.
IEEE 1901 is more or less HomePlug AV which is rated at 200Mbps, but there are optional features to go faster; how fast? Atheros announced their IEEE 1901 AR7400 chip to be 500Mbps.
Real world performance will not be the same, but for on-the-box speed IEEE 1901 wins.