Airport Extreme 802.11n 5ghz?

You are not understanding correctly how wireless works.

The 5ghz AC wireless is backwards compatible to N at whatever speed the express can connect.. usually 300mbit.

There is no need to set the 5ghz to slower speed.. it will work fine.

However the Express has limitations.. If it is the older model.. A1264 it can only do single band.. ie it either does 2.4ghz or 5ghz and the range is poor on 5ghz.

The new A1392 is dual band simultaneous.. so it can connect to the 5ghz and extend it.. that option should be available to extend both bands.

You can extend the 5ghz but only if the express is so close it probably isn't worth the effort.. and please note the actual throughput cannot exceed double hop wireless which is going to be down around 60-80mbps.. at its very best.. extend wireless cuts the speed in half.. and wireless is only half of the link speed.. Overall this is just the wrong way to do things.

If you want to maintain high speeds do not ever use wireless extend (repeater).. run ethernet or at worst.. use EOP (homeplug) adapters.. do not expect high speed over any wireless prior to AC and do expect high speed over distance.. 5ghz still has limited range.. what I call patch cord distance.

I put the Express somewhere that devices were easily connecting to the 5Ghz network and told it to ONLY extend the 5Ghz network.

The problem is that the Express is probably in the worst possible location if plugged directly into the power point..

Start with the express in the same room.. and then work out.. one room at a time.. use extension cable so you can place the express up high.. 5ghz has poor penetration of solids.. and at floor level most people have most of their stuff.. not much is bolted to the ceiling.. so if you want better range put wireless repeaters up high.

It will work.. but I would expect results commensurate with its age.. ie poor .. and poorer.. it will always work on 2.4ghz better.. due to more signal and range.

Getting half of 100mbps would still be better than getting what I'm getting on the 2.4Ghz connection...

Temporarily, power off the AirPort Express.

Move your laptop to exact location of the AirPort Express

Take a speed measurement of the 5 GHz wireless connection at that point

Take a speed measurement of the 2.4 GHz wireless connection at that point

Report on your results

The speed tests I did earlier were in the same approximate location.

And, the AirPort Express was powered off when you tested? If yes.....you need to understand that the Express can only "extend" the speed that it receives. It cannot make a slow signal go faster.

And, since the Express has no "ac" capability, it cannot extend the 5 GHz "ac" signal at all. It can "extend" a 5 GHz "n" signal, but the newer AirPort Extreme does not produce a 5 GHz "n" signal. It produces a 5 GHz "ac" signal.

If you want to extend the signals from the newer AirPort Extreme, you really need another new AirPort Extreme to do it. Even then, the extending AirPort Extreme will need to literally have line-of-sight with the other AirPort Extreme for higher speed operation. With a wall or two in the signal path, speeds will drop 50-70%.

Performance would be dramatically better if you could connect the AirPorts together using a wired Ethernet cable connection, since there is no speed loss at all through the cable....assuming your run will be less than 300 feet, or approximately 100 meters.