What is the lowest temps you can go down to(and be comfortable), without using a pad for your lower legs/feet?

I was looking to get a 50 deg. top quilt and 40 deg Phoenix for warmer temps(down to 40 deg), but dont want to add a pad to my set up, just for my legs/feet. Or am I just kidding myself b/c I really need a full length underquilt?

Maybe a piece of reflectix in my footbox would get me down to 40 deg?

-Eric