Not in AZ but posed a similar question to the WI DMV a few months ago.
Answer:
- renew before I-751, get a new license valid to end of green card (in my case added like six weeks as my DL expired on my birthday)
- renew after I-751 get an eight (yes! Eight!) year license
I did the latter and got an eight year license, which is curiously valid well beyond my extension letter.
I would recommend you file I-751 at the beginning of your window and then renew with the extension letter - they are coming pretty quick, mine was like two or three weeks back in Feb this year.