Xeons are perfectly good for gaming but do have some drawbacks as mentioned further up in the thread.
Unless you spend a stupid amount of money on an after market MOBO to over clock them, you cant. To buy a xeon with even a 3.0ghz + stock speed is nuts money, as they design these chips to run 24/7 365 days a year at 100% load. They are also much better in running VMware or other virtulization platforms.
For the cost of a modern Xeon CPU, which have there prices jacked because they are aim at the commercial market, you could build a high end gaming rig using consumer products.
You will notice the rig I have under my profile is an old dell precision workstation which is packing two xeon dual core chips, this works fine for me as a World of Warcraft rig, and I can run the game on just under ultra settings at 1600 x 1200 resolution.
In short, I wouldn't spend your money on a new Xeon chip and system as you wont get the "value add" from the system, unless as mentioned earlier, you use the PC for graphics and encoding, but a Xeon system only overtakes desktop PC's in this area when you have more than one Xeon chip in the set-up, thus utilising more logical and virtual cores.
Getting to the bottom of this thread i have just realised your not planning on buying one............. anyway you get the point