More ram on MBP 5,3

I installed Monterey on a MBP 15, 5,3 and it is running fine.
It has 2x2gb ram installed, tho. Should I upgrade it and try something an OS more recent? are there advantages?

Also, would 1600mhz ddr3 work fine or should I buy 1066mhz memory? 1600 is easier to find and way cheaper, for some reason.