IBM I520 Server VS. Intel Servers

Has anyone had to switch from an AS/400 server to an Intel based one recently?..and if so what were the factors that helped make such a determination?I have to make some upgrades soon and we have been an IBM 400 shop for many years.We have looked at the I520 server from IBM,but some people suggests we consider the intel platform.where do i can i get comparison costs/TCO information that is independent for let’s say three years on both machines?