Suggestion for max.mapred.map.tasks

[Saptarshi Guha]

Hello,
I have access to a small group of heterogenous servers:
A has four cores, 16gb
B : four such machines , eight Cores ,16gb
C: two, each with 16 Cores  and 128gb
Each of these will be tasktrackers and datanodes.
What should be the appropiate values for mapred.max.map/reduce.tasks
For A and B I have 6 and 4 respectively( yes a bit much for A), what  
is recommended for C?

Thanks and regards
Saptarshi