As you know WiFi speeds depend on both router and client working well together. I don't know if you recall the early days and "Pre-N" where things didn't work together. Who said your Asus would play well with all routers?
It's more complicated than it seems and no, changing the model for same model should result in same speeds. Changing router models is more likely to have an effect but will anyone tell you this?
Getting only 30 mbps download with on wifi with ASUS TP300LAlaptop (less than a year old) while 3 other laptops (all different makes) on the same network are getting 60 + mbps on wifi. The download speed is lower for 2.4 Hz vs. 5.2 GHz (30 vs. 10) It is the same max speed irrespective of whether one or multiple laptops are on the simultaneously on the network. The network card (b/g/n) supports speeds much higher than 100 mbps. I do get about 100 mbps through direct Ethernet connection. The upload speed is 10 mbps for all the 4 laptops.
Same difference whether using Ookla and Comcast Speed test.
Asus changed networking card and motherboard but it did not make any difference. They are offering to exchange the unit with a refurbished one.
I am not sure if exchanging will help. Any suggestions about what to do will be greatly appreciated. Thanks.