I generally stay out of threads like this, since so much depends on the goals of the owner. Yes, you're probably going to end up with wheel rates between 200 and 250 pounds per inch, but I would strongly recommend investing in a book like "Race Car Vehicle Dynamics" and following the design procedure described in Chapter 16. You'll have the satisfaction of knowing you've based your decision on a proven procedure and that the results will fall within a range corresponding to a particular class of racecar.