Home Network Question: New Router Needed? E4200V2 vs. Netgear N900

Hello All, brand new to the Forum and looking for some help here.

Forgive me, I'm not a networking guru --> I'm more the build crazy rigs, test the *** out of them, cable management freak kind of guy but networking is a whole new dimension to me.
The only exposure I've had to somewhat networking and router configuration is flashing my Asus WL520-gU with Tomato firmware... And to now I still have no idea how QoS works etc, but with time I'll try and figure it out - being a full time student I dont have much time.

At home, I have set-up a connection with ADSL (Telus...) which has been driving me crazy with slow speeds lately. I'll explain the setup, circumstance, and questions:

I have the line from the phone jack setup to the Modem from Telus (a Thompson Speedtouch... forgot the model) connected via WAN cable to my Asus WL520gU. Connected on the home network is ONE computer via Lan and on average maybe 3-4 on wireless.

Recently I have been noticing my speedtest numbers to be quite low compared to before. I am getting ~8Mbps on the LAN and ~3-4 on the wireless computers.

If i take the Router out of the equation, I can get upwards of 14-15Mbps on LAN. I'm actually signed up to be getting the Turbo Extreme service which states speeds of 20-25 Mbps... Not getting anywhere near that, but I want to make sure it's not an error on my side of the things first.

Can a router that is unable to boost a wireless signal well affect the net speeds on a wireless computer? I understand that it is a general understanding computers connected wirelessly are slower than by LAN, but by how much?

Is this an indication that the router is a source of decreased net speed? Is an upgrade to a more modern router necessary? I've been looking at the E4200V2 and Netgear N900 recently, does anyone have insight on a comparison between the two?

Thanks in advance for any advice given, and if any tips are available please feel free to let me know! I'll try my best to follow along.