REDUCED WIFI SPEED with NETGEAR R7500

It's hard to find information about the Atheros AR956x, but it appears to be a single band (2.4 GHz only), single stream 802.11n Wi-Fi adapter.  When using 20 MHz wide channels (very common with 2.4 GHz Wi-Fi when other Wi-Fi networks are present), the maximum link speed possible is 72.2 Mbps.  Real world throughput will probably be in the 25 to 35 Mbps range.  If no other Wi-Fi networks are present, then you may be able to use 40 MHz channels and a link speed of 150 Mbps.  Real world throughput will be 50% of that or less (75 Mbps or less).  But I wouldn't count on being able to use 40 MHz channels with 2.4 GHz Wi-Fi.

The Realtek RTL8192CU adapters are dual band (2.4 GHz and 5 GHz), dual stream 802.11n Wi-Fi adapters.  These should be able to connect at a link speed of 300 Mbps at 5 GHz.  Again, real world throughput will be 50% or less (150 Mbps or less).

With respect to the R7500, you will want to make sure that WMM is enabled.  Without it, Wi-Fi will slow to a crawl.  The other QoS functions, like upstream and downstream QoS, can remain off.  Since you have pretty fast Internet service (120 Mbps), you probably won't benefit from QoS, so I recommend that you leave upstream and downstream QoS off, but feel free to experiment.