> One suggests using -O3 -pipe, the other, -O2 without
> the pipe.
>
> How much difference does this make? Is the extra level
> of optimization with pipe the equivalent of the lower
> level without?

From the gcc manpage:
-pipe
Use pipes rather than temporary files for communication between the various 
stages of compilation.  This fails to work on some systems where the 
assembler is unable to read from a pipe; but the GNU assembler has no 
trouble.

The pipe is only for speeding up the compiling process. It does not speed up 
binaries. 

The -O3 contains some more optimizations than -O2, which can result in much 
bigger applications and may be contraproductive. The -O2 is widely 
recommended, but I guess you won't feel a big difference anyway. See man gcc 
for a more detailled description. 


- Sascha