AirPort Extreme: slow upload via ethernet, but fast via wireless

I’m 90% (I leave that 10% just in case) ;), that the Wi-Fi card that ships with a Mac Pro’s is not capable of sharing the ethernet connection (that connects to Internet) over the Wi-Fi in dual band mode. The reason for this is that the very same Airport Express is not able to do that (and it’s a dedicated piece of hardware). You can infer that from two things:

1. It’s not mentioned in Apple’s website that the Airport Express (or Mac Pro) have simultaneous dual band, which would be required for what you want.

2. It is mentioned that (and I quote): “Speed and range will be less if an 802.11a/b/g product joins the network”. That means, that although they can use either 2.4Ghz or 5.0Ghz, they cannot use both at the same time, and when a slower 2.4 device (using a/b/g) joins, the antenna must switch to that speed, because they only have one antenna.

The Airport Base Station (Airport Extreme), on the other hand, mentions that in the very front page: “AirPort Extreme operates in the 2.4GHz and 5GHz bands simultaneously and offers even better performance and range.”. Seeing is believing ;)

So the answer to your question is: No, the Airport Extreme card on a Mac Pro (or any other Wi-Fi Mac Computer for the matter) as of November 2010, is not capable of using a Wi-Fi connection in simultaneous dual-band; not for sharing, not as a client either.

1. TimeMachine isn't supported and doesn't like to work with drives connected to non-TimeCapsule or non-Servers.
2. The express USB only works for printers, not drives. (no file server included)
3. Turning off WiFi on the ISP router and letting Airport run either in bridge mode (letting the ISP router handle everything) is the easiest option. I prefer to have my ISP router be a bridge and let the AirPort run the network to take advantage of it's software and logging / graphing tools. Some ISP don't like that and you need them to modify their upstream device - but most just work fine.

The benefits I see on AirPort are having one strong signal (turning off the ISP WiFi) and less interference as well as simplicity of managing the AirPort software.