my experiences:
dd1: bf until 2 1/2 mos, termed ftt (undiagnosed sphincter issues) switched to formula. birthweight: 7lbs 1 oz weight at 2 1/2 mos: 9 lbs weight at 1 yr: 15lbs 14 oz current height/weight (17 1/2): 6'2" 180lbs
dd2: bf until 6 mos when she bit me (was advised by dr to switch to formula). birthweight: 6lbs 5 oz (35 wks) weight at 1 yr: 19lbs 15 oz current height/weight (almost 15 yrs): 5'11" 185lbs
ds: 30 wkr preemie, received pumped bmilk until age 8 mos, along with fortifier, then over to formula until almost age 3. was also on steroids from birth until age 3. birthweight: 3lbs 6 oz weight at 1 yr: 24 lbs current height/weight (11 1/2 yrs): 5'7" 120lbs
(new dh)
dd3: 37 wkr, IUGR, never got a drop of formula and was EBF until 6 mos when some solids were tried until she was about 18 mos before going over to actual meals. gained weight rapidly until 4 mos (was 14lbs @ 4 mos old). was bf until 26.5 mos. birthweight: 5lbs 1 oz, 17 3/4" weight at 1 yr: 18lbs 2 oz current height/weight (4 yrs): 33lbs 40"
dd4: 35 wkr, 100% bottlefed at hospital release age 17 days. bmilk + fortifiers due to a metabolic disorder. stopped fortifiers and bottles ~6 wks old. birthweight: 6lbs 7.9 oz, 19 1/2" current weight (4 1/2 mos): ~ 14.5 lbs, 25 1/4"
the youngest two were (are) bf the most and on demand. there growth is about the same as my others at this age; the first three when they were bf were bf on a schedule. the other 3 were given formula and were about the same size as dd3 at 1 and she never got formula. what cracks me up is that i was told dd4 wouldn't gain properly on my milk alone because it wasn't enough so we "had" to add the fortifier and carefully measure her intake/output. ha. oh, and my first dh id 6'3" 235lbs, new dh id 6'1" 175lbs. i'm 5'10" 180ish (usually 145-155).
so i've had really skinny ff babies, one chunky ff baby (he was on steroids, too) and skinny-then-chunky-then-skinny bf baby!