SCCA autocross allows *ANY* DOT-approved tire
Thanks for the answer to my original question, Jesse.
I researched these tires more, decided to buy them, then met with nothing but disappointment. Nobody can get their hands on them for X amount of time. One place said 2 or 3 weeks. Another said 2 or 3 months. I appreciate the honesty from the latter. I'm betting if they could keep these things in stock, Falken and Kumho would start being afraid.
I've got the 615's and love them. Price isn't really any different than the MX's. Even in my size (275/40/17) there's only about a $10 difference in price. If $40 is going to break the bank, you've picked the wrong hobby.
You're not the first person to accuse me of being chincy by a long shot. Count the pennies and the dollars will take care of themselves. Add shipping and mounting for each tire and this is about what you get for four tires.
Falken RT615: $159 ... ~$756 (vulcantire.com)
Kumho MX: $139 ... ~$676 (tirerack.com)
Hankook Z212: $106 ... ~$544 (edgeracing.com)