you must understand how most of the ram is used
generally even the fastest ddr3 ram and ddr or ddr2 ram have almost the same amount of time to access the data if processor asks data from positions in the ram which are not continuous
the difference in them is the sequential bandwidth.if processor asks the data which are side and side as an array then the speed is very high and there comes the bandwidth of the ram
suppose processor asks for memory in 10th ,99 th, 57 th postion then then for every time the data comes after the latency
if we ask as data from 34th to 500th position into cache
then the only time the latency occurs is during the fetch of the first bit of data and from there it comes at the speed of ram maximum bandwidth
so here the ram speed matters
you must also know that having ram speed more than the fsb(front side bus) do not gain anything
in most of the cases the difference in performance of programs using different speeds is not that much because they mostly access data randomly from various locations or the time(in this case low latency ram has a lot of advantage) or computation in cache is very high when compared to memory writing and reading
but the hardware, compilers , programs ... are designed to make use of memory bandwidth(to fetch memory in continuous mode )
the thing which happens is that when processor does not find the available data in its cache then it loads some amount (few kilo bytes)of continuous data which comes from ram and copied into cache then the data is modified as the program suggests and generally written into some other position in ram as the program has to do , in generally writing occurs sequential
Intel ,amd and programmers know that ram is slow in random access but in sequential access it rocks hence programmers make programs for using sequential fetch
for most of the games memory speed can increase fps(when physics in games occurs like explosions and particles fl away and gravity ...)
you just need a good gpu and faster processor to get good fps
note: more ram means more good gaming (if ram speed is near to fsb, else make a dual channel with ram)