i need to know about dual processor motherboards i forget exactly who has them but plz reply if you know anything :

1). What is the speed increase like from 1 CPU to 2 CPU - is it worth it ?
2). What are best processors for doing this - skt 940 opteron ??
3). What processor speed would be good for quick response and allowing multiple machines to connect and view large databases (maximum 8 at one time) ??
4). What sort of price is good for the processor required?
5). What motherboards are best / fastest?