theoretically yes it should be better. I think that its faster because its talking native disk language end to end. im not positive however but i will be testing that fairly soon:

dual port 4gb fiber channel VS. dual port 3gb SAS

I think SAS is more expandable by design as well. Just wait till you see SAS SAN's - people will be running back to fiber channel because it seems a heck of a lot more complex now.