8GB vs 16GB, especially for gaming you will see no difference in performance. That money would be better spent elsewhere in the build. As another poster mentioned, adding additional memory can cause instability in a system. Even identically branded sets or RAM can be incompatible and cause extremely difficult to diagnose issue and random crashing. The less RAM sticks the better is always the rule of thumb. The more DIMMs you occupy the higher likelihood that one can encounter an incompatibly issue. Overclocking can also be an issue as you will only be able to overclock as fast as the slowest stick. Faster memory could improve your performance, SLIGHTLY. From your previous post I believe that your current bottleneck is going to be your CPU more-so than anything with gaming. Grabbing 16GB of DDR3 RAM for future-proofing just isn't the way to go. If you want to get a longer lifetime out of your pc, you'll want better a better processor or graphics card. Once games will have caught up to your 16GBs of RAM, your CPU and GPU will be long obsolete. Since everything will have already moved to DDR4 or whatever it is at the time, your purchase of 16GBs of DDR3 RAM right now will have been for nothing.
In summary, no. Do not upgrade your 8GB to 16GB.