I was reading that on an average server the PLE is about 300 or 5 minutes.
Nope. Completely wrong. Anyone who says PLE should be 300 doesn't understand what PLE is.
300, or 5 minutes means you're, on average, replacing the entire size buffer pool in 5 minutes and that is incredibly high buffer pool churn for any DB. The more memory, the worst the churn.
Take the amount of memory, take the PLE in seconds and from that you can work out the average MB/sec that you'll be driving the IO subsystem. Then see how much your IO subsystem can handle.
You want that counter as high as possible. If you want a limit, then 300*(memory/4GB) is kinda an acceptable minimum, as that will be driving IO load to incredibly high values.
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