Separately installed packages will not be automatically installed in sysupgrade. You need to install them separately.
Usually settings work ok, but if there are something strange, it is usually better to configure again from scratch. Depends on quite many things and also on your skills.
Thanks again @hnyman!
I can configure it again from scratch just like I did it previous time, but it takes way too long and I do not have the time to do it every time... That's the biggest problem.
I guess I will skip the next several upgrades if upgrading with keeping the config and modules cannot be done in few simple/fast steps, and I'll try again in few months, when I will have enough time to reconfigure it from scratch if something will go wrong (again). 
(Too bad Lede is not doing the upgrades, for example, as IPFire is doing it.)
About the config of packages installed via opkg, for example i use OpenVPN and after the sysupgrade, i onlky have to opkg install the mising openvpn packages. Then magically, my config for openvpn is there, i don't have to do anything else. That is because on a sysupgrade the /etc/config directory is not wiped out (if you check the keep settings).
Also try to backup your settings and restore them after the sysupgrade, if there is any problem.
Is it possible to go from DD-WRT directly to this LEDE build or do I have to go back to stock first?
Yeah you can ssh into ddwrt and type
mtd erase linux
or maybe it was mtd erase kernel, haven't used ddwrt in a while 
then type reboot and tftp LEDE R7800 squashfs factory.img to 192.168.1.1
I use Windows built in tftp client which is really simple and reliable to just do
tftp -i 192.168.1.1 PUT lede.img
then wait 2 mins and it should be ready to login or ssh
I have been using this method for upgrading LEDE as well because I can't get sysupgrade tars to actually flash (they appear to succeed but no changes on reboot) so I have to restore the backup from fresh every time
Why bother to erase the dd-wrt kernel partition at all, if your goal is to utilise the OEM recovery TFTP mode for the actual flashing. Simply just trigger the TFTP mode manually...
On newer builds the web ui is very unstable.
Every other click only loads half a page or no page at all. Need to refresh.
Sounds strange. I have not seen that.
Yeah I have noticed that on the master builds for a while, in addition to the unstable wireless under load, that’s why I stick to stable builds.
Same as me master builds web ui is very unresponsive to the point of even a reboot cant cure it , stable builds for me too no problems there
On stable builds anyone gettimg issues with 5ghz wifi not switching to channel higher then 48?
Even if I choose 40 it stays at 48.
This may sound like a dumb question, is there a limit to what R7800 routers this build will run on, currently looking at the NetGear R7800-100UKS Nighthawk X4S AC2600 but dont want to end up buying a router that cant run a stable build on it.
Edit. Derp, that is the only R7800, im just bad at reading web pages.
So, I've tried sysupgrade, then I've installed the extra packages I normally use (openvpn and dnscrypt) and everything went well, except the Adblock was asking for a new config file (I guess something has changed in its format), but I've followed the example given there to change the config file, and so I've updated the file, and now it's ok. I like this magic, and I look forward to Lede to make the update even easier..
PS: most probably the following questions were asked before, so I apologies if I haven't found the answer in this thread, but, what is the difference between the two versions posted at the top, and can I switch between them while keeping the settings? (I am searching to have the most stable release, and I definitely want to use hnyman's version as it has almost everything I need already compiled in it.)
Thank you!
Currently there is no material difference in config files, and I am constantly jumping between master and 17.01 when I test a new build. So, in general you can keep the settings and flash the other other quite ok.
Thank you very much for your fast and clear answer, @hnyman!
It's clear: as I am just a user and not a developer, I will change now to the 17.01.3 stable branch (I use one of the Masters now).
PS: thanks again @hnyman for the great work you are doing here!
@hnyman first off, thank you so much for these custom builds and the work you've done. I was wondering if you could include the fast path patch in future builds?
I know I could build my own and I will this weekend but I thought I'd see if you'd include it which would make it easier, its the only new feature I'd need in my own build
I tested it 1-2 months ago (using dissent1's clean patch) but I did not find it useful for me, so I dropped it.
I might do a test build later, but it is no magic bullet for every speed problem. (There is probably also a reason why it is not yet included in Linux upstream by default)
I understand, I am enjoying this new router, huge upgrade from what I had especially with bufferbloat rating went from a D to a A+. However, I've lost a bit of speed and was hoping fast path would help in that regards which is why I'm curious to try it.
I have a gig connection and I'm getting around ~750 u/d on this router, used to get more on the other device around ~900 u/d. For some reason I get less on stock firmware then on LEDE for this router, I did try latest stock firmware prior to switching to this.
Edited:
forgot to throw in that I had issues with master and 5ghz, I looked at both logs and noticed the router wasn't loading a firmware file, I figured it out by making a copy of firmware-5.bin in /lib/firmware/ath10k/QCA9984/hw1.0 and naming it firmware-6.bin. It was the file the logs couldn't find and since then the 5ghz hasn't turned off at all
Weird, I'm not so experienced but I couldn't find any difference in ath10k driver between firmware-5 and firmware-6 that could improve behavior. Besides firmware-6 entry in log is a dummy entry, not causing anything in our case.
well, I didn't do anything else besides that and the 5ghz came back on and hasn't died at all since. I've been reading that it has been having issues for some. I'm on the LEDE Reboot SNAPSHOT r5095-699c6fcc31 / LuCI Master (git-17.288.58597-a47dd6e) version, haven't updated.
Do you know what I could do to improve my speeds? (besides testing fast path ofc )