It's perfectly "safe" to set most components to any settings you like, without causing actual damage to them. At worst, with setting the memory timings too agressively, you'll get corrupted data and instability and crashes, maybe need to reset the CMOS to get it to boot again if you go too far. The only way to damage memory (or the CPU for that matter), other than actually breaking them physically, is to increase the voltage too much, trying to overclock it. That's hard to do with memory, since it's really the heat problem that kills the CPU in that case.
If you've got good brand memory, like Crucial, Corsair, Mushkin, 2.5T memory will probably run just fine at CAS2. I run Crucial 2.5T at 2 in my system just fine, with all the other timings that are accessible set to their most agressive as well (which isn't really THAT aggressive on this board, but isn't slow either).