12 Months. When it's hot out (early June through Sept/Oct, get out early and head up to Payson/Pine, or Flagsaff. The rest of the time you'll be pretty comfortable in the afternoons but want a sweater/jacket in the morning. At no time will your feet be cold.
At no time of the year is your Cobra a commuter car. There is just too much traffic for the manual trans we have in our cars. You'll slip it way too much just driving. Head out of town and have fun.
I've not lived there for a long time but I know that the drive from Phoenix ("The Valley") up to Sedona - and there are probably 10 different ways with all beautiful drives - will blow your socks off. My favorite is the Wickenberug, Prescott, and then to Flagstaff and 17 back home. It's a nice (long) day drive. Stop if Flag if you stop to take lots of pictures.
Another very nice drive is the "long way" to Tucson. Don't take the freeway - go through Apache Junction, Florence... If you're not in a hurry then go through Superior, Miami, Globe and then down Christmas, etc. That route is a day trip and again stop in Tucson and come back the next day.
When I go to Phoenix from Colorado I always go south on I25 to I40 and get off at Holbrook. There is a little back road that will take you directly to Heber and then to Heber, Payson, and to north Scottsdale. It's a rarely traveled road that you can "go fast". For scenery go from Holbrook to Snowflake and ShowLow. That's the Salt River Canyon drive - fun but twisty with roads that have cliffs on one side and canyons on the other side. My mom freaked.
Then you have to take a river rafting trip on the Grand Canyon (I am waiting for my 5th permit).
Arizona is my second favorite state. I truly love Colorado - we've live here over half of our lives now - but the scenery in Arizona is so nice.