The amount of RAM does not affect speed of RAM. However, if you ran out of RAM, it will grind your system to a halt. This can happen - or not - with both 8 GB and 4 GB, depending on use. For gaming 4 GB tends to be *enough* these days.
Lots of people buy 1333mhz RAM for gaming, although 1333 to 1600 sounds like a leap it is actually quite small practically and in actual performance, however, the leap from 4gb to 8gb is quite siginificant and will literally result in near double (potential) performance, because you have double the RAM available.
Well, I would count the fact that I am able to have multiple programs open/running without running out of RAM as increasing performance...
It's all just relative to how you are classifying performance. Performance is not simply about speed, I don't care how fast that RAM is if I only have 2GB and I am trying to use 6, the "performance" of 2gb is not satisfactory for my needs. That is also why I prefaced my comment with (potential). The way he understands the performance of RAM, it is better to have 8gb at 1333 over 4gb at 1600.