^^^^^^^^^^^whens the last time a new os ran noticeably faster than its predecessor on the exact same hardware right out of the box?^^^^^^^^^^^
As a linux user you can easily answer the question yourself. :-)
Linux the kernel yes, most distros not really. Many of them have started to bloat (hence my qualifier of ‘out of the box’) Linux distros can when installed correctly (not really hard to do) improve performance in version over version but if you look at the system requirement for RHE3 vs RHEL5.1 you’ll see that required resources have increased, for a reason..