Então talvez isso seja um problema com minhas placas de Wi-Fi?
Realmente é.
In practice you're not likely to see an 802.11ac reach its theoretical maximum of 1.3 Gigabit per second (Gbps). That's because the conditions you need to reach that speed requires a laboratory not your office.
To reach the highest speeds you need three data-streams, each of which can run up to 433 Megabits per second (Mbps). A typical 802.11ac access point can support up to eight data streams. Client devices must only support one.
For example, the Samsung Galaxy S4 supports 802.11ac with the Broadcom BCM4335 Wi-Fi chipset. This chipset only supports a single stream so, even in the best of all possible worlds, you'll only see 433Mbps.
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Fonte Gigabit Wi-Fi: 802.11ac está aqui: Cinco coisas que você precisa saber