Corsair XMS are speedbinned with slightly tighter timings than value select and have a fancy heatspreader and name stamped on them, but for the most part, they are still the same poor quality ICs
Consider the following...other than SiSandra or any other benchmarking utility, you won't notice any real world difference between 2-2-2 timings and 3-3-3 timings at all whatsoever unless you're measuring load times in milliseconds or something similar. Memory latency have little impact on overall bandwidth and much greater impact on stability therefore if you are buying tighter timings you are buying them to loosen them for higher frequencies
Furthermore, your BIOS configures all memory to run at the same settings, there if your current valueselect runs at 3-3-3 it most likely cannot operate at 2-2-2 without stability issues, therefore your XMS that most likely can operate at 2-2-2 most be set at 3-3-3 to conpensate for any instability issues, negating any marginal performance gains you may see from lower latency
Heatspreaders are not an issue as unless you are overclocking your RAM isn't going to be generating any dangerous heat anyways, and heatspreaders won't really even cool down your memory substancially anyways, in most cases once you get up to 2.9vdimm you want to start actively cooling memory
You also have to consider if you really need 2GB or not and the simple fact that in my experience more memory really on increases response time when you close a game and open something up like photoshop...but other than that, it doesn't really effect much else unless you're aiming at a higher end workstation. There are still no games that don't run without more than 1GB of memory and VRAM is more important for gaming than system RAM anyways