[sounds]

I'd really like to know if the situation changes if you:

1. Disable your other airport expresses and the 2nd airport extreme

2. Place your iPad as close to the airport extreme as is reasonably possible (the one connected to the cable modem... just to try to get the max speed – it would be interesting to see what the speed dropoff with distance is in a second, separate test)

3. Try the different options again (especially connecting on 5ghz using a different SSID with the airport extreme's 5ghz network set to n-only)

It's not just the wifi interference (which shouldn't be a problem, but could you also post how many other wifi SSIDs are visible from your iPad?) – but multiple airport expresses mixed with an airport extreme falls outside the realm of what 99% of users do (I think it could be a bug when the airports interact).

As other posters have said, this kind of performance drop is abnormal.

[fields]

I will run some other tests when I get a chance. I've done #2, with no effect.

I don't think the Airport Expresses have anything to do with it - I've had some reports of other people being able to replicate my results without that.

[stock_toaster]

Have you tried using specific channels (choosing channels with less interference from other access points in your area -- i use wifi-explorer) for 5ghz and 2.4ghz, instead of leaving them at automatic?

[fields]

I have not in this case, but I've found in the past that the appropriate channels tend to shift with other usage in the area, and leaving it on automatic allows it to compensate for that, while hardcoding a channel can work for a while and then stop being the best.