For a backup device, it makes more sense to keep an identical device as cold spare, as that makes migrating configurations and debugging a lot easier. Especially in this case with swconfig (ath79) versus DSA (mt7621).
Diversifying makes sense, if…
you can trade up (c7 vs 6u is more of a side-step)
you still have old devices around 'for free', which can be jury rigged into service even if they aren't really up to keeping pace with normal production services
you aren't happy with the current device for one reason or another (giving the competition a chance)
you are familiar with the details and want a playground
there'd be a significant price delta
Admittedly, I wouldn't buy either of these devices myself. The c7 is a bit dated and imho overpriced for what it can offer (although it's still a dependable and solid device), the c6u comes with rather wonky wireless (mt7603e (bad in congested environments) + mt7613be (DSA support mostly missing), the red headed stepchildren of the mt76 family).
I keep a cold spare of same model that I run same OpenWRT on. So it just needs a config restore and you are back on track. That being said, none of my four C7's (overclocked to 1GHz!) ever failed in four years...
Well, the main driver will be the price. The C6U is half the price of the C7 and because of that I was wondering, worth it? But if it have that problems with WIFI I prefer to be sure with a backup C7.
About a new router is becoming difficult for me that. I started at some years with a WDR3600 that works well and heavy loaded. Adblock, privoxy, dnscrypt, Samba, vnstat, using the USB for overlay, logs and NAS and was the main router for a 3 floor home. I have more three router over the floors.After sometime I move to C7 and move all this to it except Samba that remains on WDR3600. Later I add raspberry PI as a PiHole, dnscrypt and NAS, removing this from C7 and WDR3600 that is only a AP.
All this to comment that I was searching around for a new one but, witch new one? With a three floor house one router never works, I need that over all floors, I move everything to raspberry PI, and so everything that I find here, OpenWRT, is to expensive to do the same as C7. And most of the routers you have on the Openwrt list I can not find here, Portugal.
I think the feeling was, what I can do with a new one! Or just have a new one!
Well, I think I am wait for Black-Friday, who knows I get a C7 cheaper LOL
I run all my C7's as APs and use 80MHz wide 5GHz channels only. With stock 720MHz clock, you run out of sirq before you run out of bandwidth. 1GHz is a sweet spot where both WiFi bandwith and CPU grunt converge...it runs flat out on both and nets 500Mbit of WiFi throughput (no NAT, just WLAN).
But even if you run it as proper router (I use x86 for that), performance scales in linear fashion. OpenVPN is faster, routing goes quicker etc. 1GHz is sweet spot. No heat or clock issues. More is possible but internal clock usually skews beyond 1GHz.
I will take a deep look on that, I never tough having routers with OC. I will make some tests here with CT drivers, no NAT, after that see what I have with no CT drivers and after see how that works with OC as you did on your post.
I am powering my C7's with PoE so I am able to measure power consumtion (through my PoE switch). Power increase by OC from 720 to 960MHz is neglible ... like 0.2W. It uses 5.4W in total with 2.4GHz switched off.
Well, i get a new Archer Archer C7 V5 and I make some tests with it, most clean possible.
I test with a laptop DELL with a Intel AC 8265 2x2 MIMO and also with a XIOMI Lite M10.
I test with Speedtest and Iperf3, Laptop and Mobile as client and a old AMD FX-4300 computer (7 years) as Iperf3 Server
This new Archer C7 is connected as a AP to a main Archer C7 that works as a router
So, I test with CT drivers and no CT drivers except with Mobile was with only CT drivers.
With CT Drivers:
Speed Test - 271 download and 105 upload (operator limit)
Client -> Server - 250Mb
Server -> Cliente (-R Swicth) - 282
Without CT Drivers
Speedtest - 241, less 30Mb
Client -> Server - 216Mb, less 34Mb
Server -> Cliente (-R Swicth) - 250, less 30Mb
For me without CT is worst
The Iperf with Xiaomi MI 10 Lite I have:
Client -> Server - 236Mb
Server -> Cliente (-R Swicth) - 233
Regarding OC after some reading I think gain does not worth the risk.