Flying along in a Cirrus at 3500 feet, still inside of Class D airspace, but switched to departure. You're at 3500 feet, in the climb to 6,500 when you look at your instruments, and the number 3 CHT has blown well past 500 degrees, and flashing red at you. Boost is already on, but you running slightly lean of peak. You push the mixture to full, with no observable difference. Suddenly, the number 3 CHT temp drops to normal, than suddenly spikes again past 500. The engine begins to run incredibly rough, and the number 3 CHT is at 0. Altitude is now 3800. Look for place to ditch? Attempt the airport? Pull the handle? Flight conditions at time of incident: VFR, daytime, clear and a million. Departed out of Ryan Field, Tucson (elevation 2417). Winds were light. I was over desert. Only real option for a ditch would have been the interstate, otherwise it was mesquite, creosote, and palo verde trees. Tell me what you'd do, and I'll tell you what I did. I'd like some feedback about what I did after I get a few replies about it.