I notice absolutely no difference between the two. There may be some synthetic benchmark by which the faster speed gets you a few more point, but other than that, you won't notice the difference in games.
There was a review of Ram speed (1333 vs 1600) performance diff, specifically for SB CPUs. It concluded that in normall day-to-day usage there was NO differnces in performance with the cavet that their were a few (very few) softare apps that could take advantage of the added bandwidth. The bottom line was "1600 was the sweet spot SB systems, but should be bought (over 1333) only if the price was nearly the same". My quess is that applies equally to amd and older Intel systems.
Additional comments on DDR3-1333 vs DDR3-1600 for Intel SB CPUs.
For Intel SB CPUs, This has been tempered recently as Intel has stated that OCed Ram voids it's warrenty. DDR3-1600 is OCed ram (exceeds the 1333 spec.
Initially the concern was based on ram Voltage as Most older DDR3-1600+ ram required 1.60 ->1.65 V. This exceeded Intel's spec of 1.50 ± 5% (max Ram V = 1.575V). Newer Ram DDR3-1600 @ 1.50 are now available (Lower CL ratings). While the 1.50 is NOW below Intels max voltage rating, Intel NOW says even at the 1.5 volts the fact that it is above the 1333 voids the warrentee. My QUESS is that the higher freq lowers the On-Die impeadance which increases current is the rational.
Intels "fix" is for users who want to OC ram but an "additional OC warrentee ($25 for the i5-2500K).
PS - I've been running DDR3-1600 CL7 Ram @ 1.60 Volts in my i5-2500k system.
I am building a new PC for diablo 3, as mine is very old!
Is it worth getting 1600 ram over 1333 if it's for gaming such as Diablo 3?
Depends, what CPU and MOBO?
The biggest impact is having too little RAM vs a slight Frequency difference, and keep in mind the 'speed' of the RAM is function of: CPU's IMC, RAM Frequency (Higher faster) and RAM CAS Timings (Lower faster). The simplest way to determine too little in Windows 7 is the 'absence' of Free memory in the Resource Manager. Currently, I recommend 8GB of RAM and the minimum for DDR3, it's cheap and you want the GPU's Shared Memory to remain at it's maximum level.