Higher speed ram works, just at a lower frequency (it gets downclocked to what the mb supports). I assume you are running a 64 bit os, because XP 32-bit only sees about 3.5GB at the most, and windows 7 32bit only sees 4GB.
There isn't really a point in buying higher speed ram unless you plan on moving it to a new MB in the future. It looks like your mb has 4 slots, so just buy another set of 2x2 (same make/model) and be done with it. Pretty much any Non-ECC, Unbuffered,1.5V DDR will be ok if you want to go to two 4GB sticks. Memory is relatively cheap now, so if you wanted to go all out, get the highest speed reasonably priced 4x4 kit you can find (price around $5/GB, so $80-90$ or less) and then you will have at least two sticks to put on a new mb in the future most likely (Ivy bridge supports 1333/1600 default).
Quote -"XP 32-bit only sees about 3.5GB at the most, and windows 7 32bit only sees 4GB" End quote
Win XP 32 Bit and Win 7 Have Identical memory limitations. That is Both will "see" 4 gigs and Both will have between 3.0 and 3.5 as Usable. 4 Gigs (limitation for 4 gigs - memory addresses that would push above 4 gigs such as GPU memory, Dos (Yes ther is a small dos address), ect.
Windows 7 just made a cosmetic change in how 4 gigs is reported - TO elieminate users asking that question!!
As To speed:
(1) Very little performance diff between 1333 and 1600.
(2) Ram will initially be set to the Default spec. IE My DDR3-1600 in my SB system will come up as 1333 and to get the rated 1600 must change to it. IE In bios select XMP, Use profile 1.
... A. For a SB system the bclk is set to 100 MHz, changing the ram from 1333 -> 1600 does NOT change the BClk therefore does NOT effect CPU speed
... B. For My I5-750. When changing the ram from 1333 -> 1600. When selecting XMP, profile 1, IT raised the Blck Freq (and memory Multiplier Ratio. This would have raised the CPU Freq (OC); HOWEVER it also lowered the CPU multiplier so that the CPU ran at it's default value.
.. Above is to explain, each MB may have slight variance of How it is implemented.
Bottom Line, if 1333 and 1600 are nearly the same price (Also CL ratings are the same) go for the 1600.
Also FWIW - I have 8 gigs Ripjaw in I5-750 and 16 Gigs in I5-2500k - All the same modules, DDR3-1600 CL7 @ 1.6 V. Not one problem and they worked well right off the Bat. NOTE: Due to SB, the recommended DIMM Voltage is 1.5 Volt (Max Intel spec is 1.575V).
Higher speed ram, like 1600 ram will also run at the default of 1333. It can be overclocked to 1600, but does not need to be.
It really is a moot point, since current intel cpu's have an excellent memory controller that does not gain significant performance benefit from higher speed ram.
You can go faster, but those options are of interest only to record seeking overclockers.
Read this: http://www.anandtech.com/show/4503/sandy-bridge-memory-...
Also, 1.5v ram dos not need fancy heat spreaders which are mostly marketing.