It may be more of a case of a snapshot in time. It may be that that 6.04 came
out at the right time for your hardware and therefore represents what your
system was like in the past. Ideally new versions should make your system work
better, but in practice changes make your hardware seem dated. This is pretty
well universal whether it is M$, Apple or Linux. Reality bites. Ubuntu moves
with the times, but our hardware keeps on getting older, like us. That will
never change.