@Xeffort 

Hi,

Can you please give an estimate of how far the distance between the router and your client device is? (meters or feet)
And how many walls are in between?

Can the client device still see the wireless network of the router from its distant location or only the wireless network of the RE305?

  @woozle 

I would say the distance between the router and the RE305 is 7 meters, with zero walls, and between the RE305 and my laptop is 5 meters with, wall between them 1 wall and 

wardrobebetweenthem.

The laptop can see the main  wireless network (AR) and see also the RE305 (AR_EXR)...

  @Xeffort 

For the enironment you've described 10 Mbps is indeed too low.

Since the client device can still see the wireless network of the router, can you tell what sort of speed do you get when connected directly, without using the RE305?

Although I will mention that 300 Mbps through the RE305 extender is illusional. I have a RE305 myself and if the router, the RE305 and the client device are all placed within the same room and only a couple of meters away from each other I am getting a maximum throughput of 250 Mbps. And from there it gets slower and slower as the distances between the three devices are increased.
The reason why Wi-Fi through a wireless range extender (also called repeater) is so much slower than what the specifications of those range extenders suggest have been explained in other threads in this forum, so I won't repeat that here.

  @woozle I getting 8mbs without using the RE305, should I just upgrade it to RE705X? I have money for this...

btw, the RE305 is 1 year old.

  @Xeffort 

I doubt the RE705X would outperform RE305 by a magnitude. If we just go by the specs, then the RE705X might end up being 2 to 3 times faster, which would still be slow overall.

I find it weird that a direct connection to the router results in the same very low speed as with the RE305 in use. A distance of 12 meters and a wall and a wardrobe in between doesn't sound too demanding.

Is there something particular about that wall? Like, is it covered with sheet metal or is it unusually thick or does it contain really dense rebar? 

  @David-TP Not only my PC, every device in my home, when I stand next to the RE305 I getting 110mbs, from the same spot I getting 300mbs from my router...

And when I first got the RE305 It goes off every two hours, and I had to playwith the versions... 

  @woozle No

  @Xeffort 

If you are getting 110 Mbps (RE305) and 300 Mbps (router) right before the wall, but only 8-10 Mbps behind that wall and the wardrobe, then I think Wi-Fi just isn't the right way to go here.

Like David-TP mentioned, Powerline could possibly be a solution here, but it's hard to predict the resulting performance in advance.

I think the only solution that could provide you the full 600 Mbps in the location behind the wall would be to install an Ethernet cable (at least Cat 5e) all the way from the main router through the wall to that location and then connect another router there that acts as a Wi-Fi access point.