I am looking for a way to track the RAM Usage History over a longer period of time than the task manager shows of 60 seconds. 

When I switch to task manager this does not give an indication of how much RAM has been used on previous applications.

One example would be playing a game on high settings that requires min 6GB RAM but when I switch to Task Manager, it shows that only 4GB is used including other background applications. I also used several other high usage applications which should push the RAM but am not able to review the performance over time.

I'm just wondering whether its worth while upgrading to 16GB of RAM from the current 8GB

GM

There are several tools that will do tha including resource monitor, windows performance recorder, Xperf, etc  I would start with resource monitor which is built in.

Consider using perfmon to assess your counters. Its quick, easy to configure and there is a ton of documentation out there on how to interface with PowerShell, VBscript, and .NET. The options are quite extensive and you customize according to your needs.