SPListItem.Item property (Guid)
Gets or sets the value that is contained by the field identified by the specified GUID.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
To improve performance and optimize the number of SQL Server queries that SharePoint Foundation must execute, use the GetItems method of the SPList class to retrieve items that are based on the value of their fields. The GetItems method allows you to specify search criteria by passing a Collaborative Application Markup Language (CAML) query through the SPQuery or SPView class. In addition, list performance may be compromised if a list contains an unnecessarily large number of fields.