On your database server, usually the biggest bottleneck is I/O. Your I/O's get executed at about 60-80 MB / sec on a typical SCSI drive.

With DB links, your biggest bottleneck is the network. Your I/O's happen at 12.5 MB / sec on a 100BaseT network. The most critical part of a distributed solution is gobs and gobs of bandwidth (Gigabit network).