luvpears:
My limit has greatly expanded as I've gotten older. 
I liked chubby in middle school. 
I liked chubby+ in high school.
I liked chunky, plump, 200-250 lbs in college. 
I liked 250+ after college. My wife has gone up to 460 lbs from an initial 320 lbs when we met. She's now down to about 390 or so.
BigFA:
I agree with the above.  I had the exact same experience as a grew older.  Started with chubby girls in middle school, and now as an older adult I find myself really turned on by heavier women.  It really depends on a woman's height and how she carries the weight.  Being a member of boards such as this for a number of years has really opened my eyes to the beauty and sexual appeal of SSBBWs.  I would have to say a range of 250 to 400 lbs. is ideal for me now.  Although I can get turned on by smaller, chubbier women as well.
All of this is so well said and identical to what I like.
I think it has to do with height and body type/figure.  I to can be attracted to a chubbier  woman but right away I start envisioning her gaining and getting fatter.  O have admired shorter women (5' 1" - 5' 3"

  pear or hourglass figure in my eyes usually between 230-300+ Lbs.  As taller same body type 270-370 + Lbs.