54Mbps isn't, it's more like 20-22 at best. N is the same way, half or less than the advertised throughput. ac will be the same I'm sure.
I have a 1Gb cat6e network through my house. Run multiple PS3's and many many other devices, mostly cabled. Got three tablets and two sony dash's that stream netflix via the wireless. I can stream uncompressed bluray rips to multiple outputs at the same time via the cabled network. I would never try this with wireless. 5Ghz makes it slightly more stable I'm sure, but a single dropout would be enough to drive me insane.
Wireless is fine for web browsing, low res streaming, and small file transfers, that's about it. Unless you have a lot of free time on your hands.....