Processor Cores: Generally, the higher the number of cores, the more likely will the VPS be able to handle its computational operations. They also determine how fast a webpage could load(also dependent on network speed).
RAM: If you will need to store large variables then more memory will serve you better.
Caching a website is also memory intensive. Reading from a hard drive is a lot slower than reading from RAM. This is why caching is so fast. Caching stores data in the RAM and serves it directly from the RAM.
