Like the previous poster replied - follow TCAS command, taking whatever performance the aircraft gives to you.
Matters like this are addressed in an excellent way in the ACAS bulletins published by Eurocontrol, use the following link
EUROCONTROL - ACAS II Bulletins and Safety Messages
Underlying address is as follows, should the link work incorrectly from your browser. On the page that you reach with the address below, you will find a link to the 10 bulletins that have been published to date.
http://www.eurocontrol.int/msa
edit: corrected address specification