Rosscoe and Overrun,
I think that there are additional factors that need considering.
If you are looking at the QF aircraft they have the winglets which give improved climb with more flap - flap 25 would probably be the go.
You will find i think that this flap setting will give you what you need to operate viably.
VB has two types of 800's, mdeium gross weight ones with 24k motors, and high gross weight ones with 26k motors, running where possible at 24K.
All but one of the 800 HGW has winglets.