I got a copy of gcc-i2.6.3 off of sunsite a while back and
have used it extensively. The -mpentium switch works,
but reliably only with -O2. Some codes speed up 20%,
while others slow down a trifle compared with -m486 -O4.
So it's a moderately mixed bag. I use it for somethings,
and don't bother for others.