The King headset is bling, and not very good value for the money, IMHO. A Cane Creek/FSA/etc. cartridge bearing headset will work just fine, assuming that it is installed and adjusted properly [which goes for any bearing assembly]. I'll second the wheels/brakes upgrade. It will make a huge difference in your riding. I would also upgrade the shift pods to XT if you have the $$. The shifter will make the most difference to how well your bike shifts, assuming your derailleurs aren't damaged/filthy. YMMV.