Hi Anna -
good luck tonight.
I'm a true believer in bf babies never going 12 hrs at night till they are getting really decent soilds in them 3 times a day so I kept the DF (or early NF for those who don't DF) till 10-10.5 mths.
I also believe that the bigger the baby, the more they CAN take in at any one feed - once trained to do so. I had 98centilers as well and it was only by feeding at the end of naps and getting really good feeds into them (in O's case it was 15 mins, in E's only 5-7 but totally concentrated rather than bobbing on and off, 5-7mins) that we moved to 4 hr EASY and remained STTN with the help of the DF.
I think you are doing the right thing and I hope, hope, hope it works for you xxx