I have a TP-link Archer C2600 previously running 17.01.4 Luci-Lede.. was looking around for an updated package and 19 seemed better than 17.01.6.. but I guess I learnt these are not the same. :E So anyway I realised this too late and my device hasn't come back up after applying the sysupgrade.
Is there still hope? Can someone point me to either hopeful and easy or sure-thing-but-complicated restoration procedures..?
I've had success with TFTP several times when in need of a recover
I would start by trying https://openwrt.org/docs/guide-user/troubleshooting/failsafe_and_factory_reset, as I assume you're 'just' having problems with your old, 17.01 based, configuration. I that doesn't help, push-button tftp recovery with the OpenWrt 19.07.x factory image should be available; 19.07 is generally known to work on your device.
What's the consensus at the moment, is v19 OpenWRT or v17.01.6 Lede more interesting/powerful/reliable for this device? I forget exactly why I went for the Lede initially.. I'm not really using any advanced features at the moment though I have a feeling only the Lede would allow me to pump the mW up to 1000.. I really don't remember :E
A router is a very security sensitive component of your network, you should always run the most current stable release (or newer snapshots) on your device and keep it updated.
Of course. But they are different products and branches, no? Lede 17.01.6 is from September 3. OpenWRT 19.07.4 is September 10. It's not like one is lagging seriously behind the other, at least time-wise.
Alongside what @slh said, I get the following with C2600 on 19.*:
Of course. But they are different products and branches, no? Lede 17.01.6 is from September 3. OpenWRT 19.07.4 is September 10. It's not like one is lagging seriously behind the other, at least time-wise.
17.01.6 is two years old.
same month, diff year.
Ahhh... wrong year 
:E Is there a better version then, 18-something for now? I never had issues with the v17 Lede although I could never get it to beat the stock ISP modem in absolute throughput, which was kinda the point 
I always had issues with mine, so I can't really say. Varying yields of instability you might say.
You should be able to jump between versions by flashing the sysupgrade firmware for your device. Best way to find out is to test it.
Before flashing I'd backup the configuration, mark it with a firmware version number and then try the latest firmware without keeping configuration. Moving from 17. to 19. with old config might create more issues than it solves. If you find that it's worse, you can go back to your old firmware and restore your old config.
If you try 19.*, and have reboot issues, put the following in your /etc/rc.local:
echo "performance" > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
echo "performance" > /sys/devices/system/cpu/cpufreq/policy1/scaling_governor
exit 0
LEDE is no more. The name was formed when OpenWrt was branched, but then it was merged back since then. So it's safe to consider that OpenWrt and LEDE are the same thing; except that some versions are older than others.
Ideally you would want to have the most recent version which is currently 19.07.4. Your device is a common model and the image should be fine and well tested by many users.
OK seems that after some time it has managed to come back up on its own, with the new 19.07 so that's good. But I don't seem to be able to find the 1000mw/30db transmission power setting that I had set previously?
I don't own this particular device so I can't tell the hardware maximum transmit power and whether there was change in the drivers between versions that could affect that, so maybe someone who owns the same device can address that.
However, what I can tell you is that generally the transmit power is region-dependent, as it's regulated. You can test that by checking what region allows 1000mW for the same of trail only, but for your actual use you should stick to the actual region where you are located to avoid being in breach of the local regulations.
Well I having been switching the regions around and can't find any that go above 20db100mw now. Weird as this seems to keep changing 
In another case on my BCM4708 running DDWRT the 300mw setting is actually faster than using it at 900, from the particular PC I'm testing with in any case.
But no region I'm trying at the moment is allowing me to use more than 100mw which is very odd.
Oh, setting US allows me me to 23db/199mw, that's something..
Sometimes increasing the power allegedly increases the noise more than it increases the range. Note that while you increase the transmit power of the router, the clients' transmit power remain the same.
The other downside of increasing the power beyond hardware default is the it could overheats the device which could lead to premature failure.
I am not saying you shouldn't try to adjust power; it's certainly one good option in custom firmwares. I am saying that it's not always the answer--not the extreme range such as 1000mW anyway.
Well I wouldn't mind getting it up to 25db or 600-ish mW though.. but the firmware doesn't seem to want to give it to me anymore