No one deserves to get ripped off, but with secondhand deals you have to do more research.
There's only so much you can test when buying second hand, people have lives and they can't dedicate hours to sell something 2nd hand. I was able to run the card, reboot a system and see it post. The XT part was not part of the scam (maybe it was intended to), I figured that out quickly and renegotiated the price. It's just backstory to give enough context, since the guy appeared to not be aware it was a non-XT.
Also yes, the core clocks tend to run ~25MHz slower than set by the driver, and the memory is about 2-4MHz out. These are my cores at "1266" and I set memory at 1864 or 1784 to get the actual clocks I want on the memory.
That's great news, then the card has been acting exactly as it should for the past 18:30h. Yep, new stability record broken. Now let's see if it can handle a cool-off reboot and still POST, will try after work - for now leave it mining! It has paid 6 euro for itself already, only 664 eur to go and it wasn't that useless and dead afterall

I will still test it gaming too, didn't have the time yet but next weekend for sure.
I wouldn't be surprised if a BIOS-modded card with double or triple the tREF value just straight-up crashes out of games constantly. People who have bought used ex-mining cards often complain of crashes, texture corruption and artifacts in game. That's not specific to the 5700-series, just ex-mining cards in general. I presume all mining BIOSes increase tREF which, presumably, is set very short by default for stability in mixed workloads (rather than the 100% 24/7 VRAM workout that ETH mining is).
Might not be entirely the case. The looser and oldschool way for polaris cards wouldn't increase the tRef on higher clocks, simply copying the exact timming string from 1500 and pasting in the higher clocks' timings was enough (maybe the tRef can be further increased but back then no1 figured that out at least). Isn't the timming string just a hash or hex of the full timmings table? If that's so, then modding the 500 series would actually decrease the tRef, since they seem to be always higher on higher clocks' timmings but if you were copying the 1500 for all others, you'd be using the tRef from 1500 which is certainly lower than the 1750 and so on. I recently sold my old RX 570 that mined back in 2018 since they were in such a good state. The same hardware shop that reflowed my GPU assembles gaming PCs so I gave them the cards for a low price with the guarantee they will only be used for gaming PCs.. trying to give back since I was part of the beginnings of this shortage back then
I can get up to 51 with an overclock/undervolt. Usually just end up running it undervolted only at 48mh to lower temps and power since my 5700 has a bad cooler.
Sounds about right, same I was getting before I modded the bios. Just be careful and save your original bios with ATIFlash, dont use GPUZ as it will give you a 512kb version that will result in your card not POSTing. If that happens feel free to message me if you don't find enough info in this thread.. I was always able to flash the bios even with the card seemingly dead and not POSTing by running IGP as primary and force flashing with 2.93+ CLI (plus is crucial here, the normal version won't work).
Also, increasing the timmings and/or specifically the tRef will not increase temperatures. Temps only go up if voltage goes up and the 5700 mems already run at max voltage (and I don't recomend undervolting the mems on a non-XT), faster timings might cause more instability, but not more heat. Core can be underclocked and undervolted for ETH with or without modded bios, again you're not touching anything related to core in the bios, it already allows pretty low voltage in the stock bios and you can't even run it stable that low so you're well within the limits with stock core settings *mine is running so far stable at 850mV on core,
@Chrispy_ seems to run them at 875 which is still pretty low, stock clock voltage can go up to 1.25v or so!
If you are comfortable with it and didn't do it yet, I recommend replacing the thermal pads, doing it correctly (not easy to find for 5700 but it's out there) decreased my mem temps from 100-105 (possibly more, but I'd stop it at 104) to 80-82. Here's a pic to demonstrate that:
If it didn't pass the 80 for 18h, it won't pass it now. Of course this is winter temps, my house is permanently at 21.5 celcius. We don't have hot summers here, but I doubt it will keep he 80 if the temps go past 25-26C, will probably go up to the 90s and stay there if air flow is proper. I could run the fan faster and achieve a lower core temp (65 is core, 80 is mems), but this fan makes a ridiculous noise already at 76%, it's unbearable at 90%+. It's also so bloody fast (almost 5k RPM) that I didn't want the card to vibrate that much until I identified where the issue is (still unsure if I did but it seems so).
Ah, you're mining on Windows of course.
That'll slow you down a bit too; Hashrates are usually quoted for Linux which is just faster for whatever reason. I guess you could dual-boot into HiveOS or even run it off a memory stick if you fancy dabbling with a dedicated linux mining distro.
Yeah this is a long running debate.. Linux seems more stable (and I can confirm with this card it IS), but all benchmarks show higher MH/s on windows. Question is if those benchmarks ensured stability or if they just ran a 30min/1hr test or so. I've had cards before that looked stable with certain configs but would crash 10h later (on windows) and we all know that's not stable mining

So far from my previous experience in 2018 and the past few nightmarish days with the 5700, linux might have 0.5-1.5MH/s less in benchmarks, but you will be able to mine on them N days straight until whatever automated cool-off time period you prefer (my 570s used to run 5 days, shutdown and cool-off 30 sec and boot).
Edit: I also did some tests some time ago on my 3060 Ti LHR, waaay more stable in linux too. It could be the specific driver versions hiveos uses, I didn't have the patience to try all of that in windows as this is my gaming card and I was just curious how the latest LHR unlock was performing when t-rex launched their latest improvement on LHR unlock. The card wouldn't even mine 1hr on windows, with the exact same settings on linux I was seeing less LHR locks triggered while achieving the same or more hashrate and same power consumption.