This isn't for cams, just my main PC that needs an upgrade which is currently an old HP Elitebook 8440 with an i5-520M CPU. I ended up snagging an HP SFF 290 with the i7-8700 3.2ghz for what I think was an absolute steal at 300 bucks and free shipping. It comes with a 256gb SSD and 8gb RAM, both of which I will replace/upgrade with 32gb RAM and add a 2TB 3.5" SATA drive for files. When looking at performance, I go by the number value assigned for the PassMark CPU benchmark. Seeing how my current CPU is 1694, and the i7-8700 is 13,120, I think it should be quite the improvement.
My cams run on an old HP M7-1015DX laptop with the i7-3610QM processor and that thing sings all day with 16 cams at about 12% CPU.