A little help needed guys.

I'm trying to decide which underquilt to get between a 40* Phoenix overstuffed with 2oz or just a standard 20*. Most of the camping I do has night time temps between 40*-60* but I would like to start stretching it to 30*. I will rarely go below 30* and when I do I won't mind using a pad. I love sleeping in the the cold but hate a cold back when doing so.

Any suggestions would be appreciated.