Hmmm?? Boeing say the normal flap is 25 or 30 for landing and the aircraft should be stabilised by 1000 AGL. IMC and 500 AGL VMC. The 777 FCTM Chapter 5 sets out the requirements for a " stabilised approach", one of which is the correct landing flap, Selecting flap 30 from 25 or visa versa is not a good idea. Also, the sideslip technique is to be removed form the FCTM and QRH limitations as Boeing now state " Crab" is the safer method and as it affords a greater XWC, on all boeings, this is to become the normal method in training.
Ex: 777 XWC limit DRY RW Crab 45 KTS, Sideslip 31 kts (772), 35KTS (773) ,
Landing distance and Vref also vary with flap, Vref by about 8 kts, so if you alnd F30 with F25 Verf inc the A/T addition, you are 13 kts into the max 20 Kts allowed on Vref.. Easier to fly it as Mr Boeing wants, saves Tea and No biscuits with the Boss