Cisco Linksys E4200 TuneUp
I have a two router set-up, an Eircom Fiber modem which takes in the connection from the phone line and a Linksys E4200 running DD-WRT plugged into it. I gave up on trying to get the Eircom router to not be a DHCP server and as a result run 2 separate LANs with nothing connected to the Eircom LAN apart from the Linksys one. Since both modems run their own Wifi networks, I can connect to both from my laptop and figured out after a while that the Linksys was only providing a fraction of the speed reflected by the Eircom modem.
I followed the instructions in the following links with pretty impressive results (download speed coming up from 3 Mbps to 12 Mbs, upload speed shooting from Kbs to 4 Mbps)
https://www.stevejenkins.com/blog/2013/01/my-cisco-linksys-e4200-dd-wrt-settings-for-max-speed/