I have not used a one wire device but I will take a shot.

I think the speed is something you do not worry about, it is part of the OWOUT command.
From the data sheet.
TRANSACTION SEQUENCE
The protocol for accessing the DS2781 through the 1-Wire port is as follows:
􀂃 Initialization
􀂃 Net Address Command
􀂃 Function Command
􀂃 Transaction/Data
This makes me think Mode 0 would be used.

Does that sound correct to anyone?