I thought that if I used WDS I would lose some bandwidth to sync functions, but would keep most of the "n" rate for data transfer.
Unfortunately, WDS only operates on "g" wireless, so your
entire network will drop to "g" levels. As I mentioned, the bandwidth loss will be tremendous in a WDS setup. Think of it this way:
"G" wireless is capable of 54 Mbps. But, you'll lose 75% of this bandwidth on the entire network if you use WDS, so the end result will be a network with about 13 Mbps capability. Any data transfers (and Time Machine backups) are going to be incredibly slow using wireless. Regular "n" is around 130 Mbps by contrast.
Short of drilling holes and running CAT 5 from the attic, what are my options.
Ethernet is always the best way to connect devices, especially if you are setting up wireless access points, so I would first investigate the feasibility of running the cable. This is the way commercial networks are designed and it provides the best bandwidth preservation and speeds on the network.
If you can't run the ethernet cable(s), take a look at a pair of ethernet powerline adapters to accomplish the same task be sending the ethernet signal over the AC wiring in your home. They work great. Faster and far more reliable than wireless.
The best performing network would have ethernet connections going to both AirPort Extremes. You could do this by simply adding a third etherent powerline adapter.
Or, run ethernet to an AirPort Extreme that is centrally located and then set that device up to allow itself to be extended and then setup the third Extreme to "extend a wireless network". The "extend" setup preserves "n" speeds on your network. You'll have 10 times faster speeds than a WDS setup.
