I'm buying an AC1300 adapter. Should I replace my N300 router?

I'm getting the Asus PCE-AC56 PCIe Adapter - $51 - which is rated at AC1300 (i.e., 400 Mbps @ 2.4GHz + 867 Mbps @ 5GHz) for my desktop located about 10 meters away from the router position passing through 2 concrete walls. I have read some articles that the 5GHz band is not good if the adapter is located far from the router.

Our old and current router is a D-Link DIR-605L Cloud Router which is rated only at N300 (300 Mbps @ 2.4GHz) - single band. We have about 4-6 laptops/phones/desktop connected to this current router. Signal strength is always Excellent in this current router wherever I position my laptops/phones around the house.

My question is: with my new AC1300 dual-band adapter, should I buy another router - or - should I keep our current router?

If buying a new router is necessary, a list of available router ratings in our location are as follows, which one would you choose and why?
AC1900 (600Mbps @ 2.4GHz + 1300Mbps @ 5GHz) - $220
AC1750 (450Mbps @ 2.4GHz + 1300Mbps @ 5GHz) - $115-$135
AC1200 (300Mbps @ 2.4GHz + 867Mbps @ 5GHz) - $85
AC750 (300Mbps @ 2.4GHz + 433Mbps @ 5GHz) - $50
N900 (450Mbps @ 2.4GHz + 450Mbps @ 5GHz) - $155
N600 (300Mbps @ 2.4GHz + 300Mbps @ 5GHz) - $120
N600 (600Mbps @ 2.4GHz) - $100

Will the 5GHz band be a factor since my desktop is away from the router? And given that my current wifi signal is always excellent, should I stick with the N connectivity?
 
Solution
The entire 5ghz thing is pointless for you because your current router does not have a 5ghz band.

You will not receive one single bennifit from getting this high end wifi card without replacing your router.

First of all, I would just get an av600 powerline adapter which will give you real speed of about 100mbps with better ping/lower latency then wifi can.
That 867mbps is max theoretical value. First of all half is for transmit and half is for receive thus it immediately gets cut in half to 432mbps. 5ft from router with perfect line of sight this more like 300 real speed. Add in 2 walls on 5ghz band and you might get 60-100.

Now a better router could benefit you just in processing performance.
Here is my recommendations. I...
The entire 5ghz thing is pointless for you because your current router does not have a 5ghz band.

You will not receive one single bennifit from getting this high end wifi card without replacing your router.

First of all, I would just get an av600 powerline adapter which will give you real speed of about 100mbps with better ping/lower latency then wifi can.
That 867mbps is max theoretical value. First of all half is for transmit and half is for receive thus it immediately gets cut in half to 432mbps. 5ft from router with perfect line of sight this more like 300 real speed. Add in 2 walls on 5ghz band and you might get 60-100.

Now a better router could benefit you just in processing performance.
Here is my recommendations. I don't like to break it out by speed because those numbers are prefect lab conditions and are completely dependent on what your devices have in them for wifi chips.
GOOD: TP-LINK WDR3600 or 4300 (whichever is on sale for cheaper) = $50 (3600 = N600, 4300 = N750)
BETTER: TP-LINK C7 ARCHER - $100 AC1750
BEST: ASUS RT-AC68U - $150-180 AC1900. The AC68R and W are the same. There is a AC68Uv2 or AC68P which is the same model with faster processor.
Last weekend Newegg had a refurb model of the 68P for $120.
 
Solution