H81 is a little on the lower end, but it technically should support a Xeon, which would likely be your best option. You can't do any overclocking with the Xeon, or your H81 board. The Z series boards allow for overclocking, just as the K series Intel CPUs allow for overclocking. So pairing an i5-4670k with an H81 is a waste of money as you won't be able to overclock. That is, unless you plan on buying a Z87/97 board in the future, then it could be worth it. But for the most part, the Xeon will do just as well as the i5.