In the same room with no interference, what's the actual possible data transfer in Mb/s from a mac connected via Ethernet to airport extreme with a wireless bridge to an airport express with Ethernet connected to a mac mini? Both are wireless N capable. I know what wireless N can do - but does the conversion from wired to wireless to wired add a lot of overhead/performance reduction?
The distance apart is 35 feet.
If you run them at 2.4GHz, you'll have a wireless link of 150mbps. If you run them at 5Ghz, you should link at 240-300mbps.
The lowest common link speed is 100mbps, due to the 10/100 port mentioned by dXTC. But that's not data.
After protocol overhead, at the OSI application layer, you're probably looking at 80mbps (or 10MB/s) data throughput.
That's if you are having the Express "join" the Extreme.
If you have the Express "expand" the Extreme's network, cut those numbers in half due to WDS overhead.
The wired-wireless conversion itself doesn't add any performance reduction, other than some negligible latency.