I don't have a "backup GPU" for my main system, but I have an entire backup computer on my KVM only a few button presses away. That computer uses 3x GeForce GTX680 in SLI. Aside from not having DX12 or Freesync support, the 3x GTX680s still do very well in the games that I care about.
The 680s carried me along for many years. I got the first one as a replacment for the 2x 4870x2 in quad-crossfire that I was running before. Then I got a 2nd GTX 680 not long afterward. I ran that 2-way SLI setup for a few years. Right about when I was going to replace those with a newer single card was when the first crypto mining boom occured. Instead of paying the inflated prices for a new card, I just got a 3rd GTX 680 instead. Used that triple-SLI setup until I got my 2080.
He lost performance because the stock pads can't be re-used. They compress way too much. There was no "Memory junction temperature" back then, so he was probably phantom throttling (or even had a large core to core hotspot delta!) and didn't even know it.
Proof? I've opened my 3090 FE over 15 times now (various repastes, shunt mods, fixing shunt mods, removing MG842AR silver paint for proper shunt mods, proper thermal pads on my very last disassembly 13 days ago (FINALLY got the core to core hotspot delta to not degrade anymore after switching from Thermalright Odyssey 1.5mm pads to Gelid Extreme 1.5mm pads!!). Gelid Extremes, NOT Gelid Ultimates.
Or if you want to wait, you can get 120mm * 120mm giant sized samples from Aliexpress.
One whole pack can do the VRAM chips on one side of the card. So that will take 2 packs for both sides' VRAM chips only.
The third pack you will need for the GPU Side VRM strips. Then you will use the leftovers from the three packs + the 4th pack for the PCB hotspots on the backplate side.