Hey folks. I've got a 700mbps connection at home. Before installing OpenWRT (18.06.02) I was getting 700Mbps both ways reliably with the original firmware.
But now my speed doesn't go above 270.
The only package I've installed is adblock. I didn't change the settings. No new devices were connected
You need to install Openwrt with the 4.14 kernel and enable flow offloading to get this speed.
But how do I get 18.06.2 with the kernel 4.14? Currently mine is on version 4.9.152
.
Also, how do I enable flow offloading?
There is no prebuilt image available now. Normally i would suggest to install a master snapshot, but it seems that offloading may be broken on the 4.19 kernel for a while.
A good way for now is to build 19.07 branch.
Or wait for the 19.07 release.
OpenWrt 18.06 does not support the hardware acceleration engine it was using with the stock firmware.
In this thread there are custom builds and instructions that enable it Ath79 builds with all kmod packages through opkg [flow offloading]
Otherwise you need to wait for OpenWrt 19.07 release
This topic is obsolete now.
it will become obsolete when 19.07 is released, most people aren't building stuff from source you know.
It is obsolete now because TS stopped building images.
Now there are two options: build 19.07, or master with 4.14 kernel.
So, considering I'm not keen on bricking my router, I better wait for the 19.07 release?
This is not a matter of bricking. It is a matter how easy for you is to build an image yourself. And what is your priority.
For me it is quite easy to build. and that is not an issue at all. I am already using it on many devices.
I expect RC builds to appear very soon for download.
I can build an 19.07 image for your device, but packages are not available in the repos for install.
So I won't get Adblock?
Also, how soon, like a week or two weeks until RC is out?
I can build with adblock 
It is quite easy when you have buildroot installed.
I think it is a matter of weeks when they setup buildbot to build 19.07 instead of 17.01. But you never know.
So ping me, and you'll get an image in ~30 min.
Thank you for the offer, I really appreciate it. But I don't want to risk breaking my device.
I'll wait, if it's just a few weeks.
Overall, with a 700 Mb line, OpenWrt will be happier on something with more CPU than the WDR3600's single-core MIPS.
OK. No problem. You never really know. It was initially scheduled for March. 
With flow offloading it should be OK, if no other heavy tasks.
It worked fine on the original firmware. OpenWRT is supposed to be superior, isn't it?
No, it isn't. Factory firmware could use hsrdware NAT that is not available on Openwrt. But with offloading most likely it will be not worse.
Openwrt is much more flexible, but not always faster.