I had CCACHE=50GB at one point, but then I repartitioned my main boot drive and forgot to add it back in so my cache was sitting at 5GB with a 38% hit rate. However, even before when it was 50GB, it would still take 8 to 10 hours to compile. Unfortunately, I didn't look at the cache hit rate stats back then so I have no idea.
My build machine is a i5 660 @ 3.33Ghz, 12GB DRAM and multiple used 250GB to 500GB hard drives that I recently bought for $2.50 CAD each.
I tend to use older hardware that I get for free because they are broken and require repair or buy them for very little money. I get the most use out of them by using lean OS and lean applications.
For my i5 660 compile machine, it cost me $10 CAD with 4GB DRAM + no hard drive. This is the fastest computer I have at home. I have multiple computers at home for use, but most are older Intel duo core E8500 with 2GB to 4GB DRAM. They work perfectly fine for my simplistic use.
I just updated 2 of my roms with the latest Jan 2021 patches. Both builds were untouched since the Dec 2020 security patches until I did a repo sync today.
SM-T350. Compiler needed to compile over 5,000 files (out of 70,000).
#### build completed successfully (01:33:44 (hh:mm:ss)) ####
SM-T560NU. Compiler needed to compile over 5,000 files (out of 70,000).
#### build completed successfully (01:37:24 (hh:mm:ss)) ####
I have 2 more roms to build as I write this. I suspect both will take roughly 90+ minutes each as well. I use one hard drive for each rom so I can keep all the changes separate.
If this were my "day job", I would invest in a faster machine, 32GB DRAM and multiple 1TB SSD drives. I have learned to schedule my day around compile times.