First of all, post some pics!!! I'm building my X3 for just about the same thing, and this sounds very interesting. I know there are a few other X3 owners here that race them and would also love to see your creation.
As for your question, the older Tiburons and Elantras share the same 4x114.3 bolt pattern. However, since you have an X3, you have to worry about the captive rotor issue unless you've swapped them out. I have a set of Tiburon wheels on my 98 Accent and they are a nice improvement from the stock 13" donuts, wallet friendly also. I'm not sure about what other makes other than Hyundai share this bolt patter, but I know there are more than a few.