I had been using a 660ti and noticed my system memory getting up to and holding around 7.1GB of 8 when playing BF4. Then I bought a new 280x and noticed that my Max memory never breaks 6.4GB. Am I missing something? Now it is around 6.1GB max and it used to be around 7.1GB. Why the sudden drop?
No game, by itself will use more than 2-3gb of ram.
With 8gb, windows is keeping more of the extra in ram on speculation that it might be reused.
The max used has no impact on performance.
It is just a measure of how high the line got before windows cleared out some ram space in case it might be needed.
If your demand page faults increase, that is a performance problem.
IN task manager/resource manager monitor Hard page faults per second. It should be near zero if you have sufficient ram.