Rebuilding packages

[WipeOut]

Most packages for most distro's seem to be compiled for i386.. Obviously 
this is for comparibility with older systems but surely this has a 
performance implication..

So the question is..
1.Does anyone rebuild their Fedora RPM's from SRPM's for i686 or 
pentium4 or athon-xp??
2. If you do, where can I find how to do it?? (or is is simply by typing 
"rpmbuild --rebuild package.srpm" )
3 Is there any advantage to doing this? (specifically for server 
packages eg Apache, MySQL, PHP)

later..