Everything you need to know is here:
http://forums.anandtech.com/showthread.php?t=2335636
Intel specs (what they publish) here:
http://ark.intel.com/products/47922/Intel-Xeon-Processor-X5650-12M-Cache-2_66-GHz-6_40-GTs-Intel-QPI
Seriously, it's worth reading through it, even if you spread that out over a few days/weeks.
I'm a firm believer that you really shouldn't overclock if you don't understand what you're doing. Chances are that doing nothing more than changing the bclk and CPU multis won't kill a system... but it could. More likely it might degrade the system over time. By default many voltages are set to auto, meaning the Mobo will automatically boost various voltages, within what it thinks is reason (remember, what if the Mobo doesn't officially support the CPU? What if there's a bug in that version of the bios?), to keep the system from crashing. And changing the BCLK changes all sorts of things in the system as many of the subsystems (cpu, RAM, uncore, QPI) are run as multipliers of the BCLK. So even if you only change that one value... you'll change a bunch of other values indirectly, and then the Mobo will start boosting voltages to try to keep those things from crashing. The mobo might also give these components more voltage than needed for stability... causing your system to run far hotter than necessary (including onboard chips that may not have active cooling and whose temperatures aren't super easily monitored). After all, running a BCLK of 211 is actually quite high... if that's all you changed your uncore and RAM might be running at really high speeds as well (I am not familiar with your board or bios, so I can't say).
Every chip series has it's own unique qualities, and every chip (even the exact same models) have different luck when it comes to voltages, heat, and stability. These 95W Xeon 5600-series are only in spec if they get less than 1.35v on the CPU. Some people report that they one should also keep the QPI/VTT Core at or below 1.35v as well, and that the RAM voltages (DIMM) need to be within .5v of the QPI/VTT Core voltages, specially if you're boosting the RAM voltages above their on rated voltage values. Apparently 5600 Xeons run the uncore, by default, at 1.5x the RAM speeds to protect the CPU's memory controller (IMC), but most people are fine running up to 2x (on the I7-9xx chips the recommended value was 2x +1).
These are the sorts of random bits of info that are wise to know, and make sure you system stays within, in order to safely overclock. Yes, you can get away with a lot-- these chips and mobos are actually very, very hardy (see people who have run 1.40v through cpu, and 1.375v through QPI/VTT core, and 1.8v through DIMMs)-- but I, personally, don't want to take the risk that I'm unknowingly doing something that might shorten the life of my system, whether it is by running borderline dangerous voltages, or running a system hotter than needed.
I think the monitoring tools are better for Windows. But you can boot into the BIOS and usually get a reported voltage while in the Bios, and you can use iState Menus or HWMonitor to see voltages as reported in OS X. You can test memory using Prime95 (there's a Mac version) or Memtest+ (bootable usb/CD).
