If it should sadly come to replacing the more workloadish parts of the PC (after the PSU), it's good to keep a couple of things in mind:
- SL does not care about your cores. The CPU that runs SL best is the CPU with the most gigamegahurtz*. SL will not care if you have 4, 6, or 18 cores. As pretty much all new processors these days come with 4+ cores, ignore any core considerations if your main focus is SL. Check how many GHz the CPU will turboboost to on ~2 cores load.
- If you have a tool to check your GPU (not CPU!) usage, open it, push it to the side, but then focus on SL and go first to a calm and quiet area and wait for things to have loaded, then to a busy-ish area and observe for a while.
Do keep SL focused (i.e. clicked into). If your GPU is not near 100%, your limiting factor at the time is the CPU. if the GPU is close to that 100% mark, the bottleneck is the GPU.
Windows 10 lets you monitor this without any special tools right in the task manager, it's the 'GPU - 3D' column. Just, as I said, make sure you are clicked into SL, else SL will lower the FPS and thus the CPU/GPU usage.
Ignore the processor usage itself, since SL will - while in focus - always nom a bit more than 100% of one core worth of CPU time. Doesn't matter what you put into your machine. (This would display as, say, ~27-30% CPU usage in a 4 core machine in the task manager)
*The efficiency of the gigamegahurtz, in simple laymen's terms, usually gets better from generation to generation of CPU, and usually it's silly to compare CPUs between generations (or Intel vs. AMD) directly/only by that metric - to a degree. But for SL the general rule of the thumb stands if the CPUs aren't multiple generations apart.
EDIT (Added a GPU thing):
Not only pretty much disregard the core count of any new CPU if your main/exclusive focus is SL when it comes to gaming...ish...things (#notagame), but also you can pretty much disregard the memory of any newish GPU. SL runs fine and dandy on a GPU with ~3GB of memory and won't really make use of more than that. Most newer GPUs come with more than that, nor will SL make use of any super special features so.....yeah. Like with the CPU, it's the raw speed that matters.
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