Cat6 cables useful?

I guess this is off-topic, but I AM using cables to interconnect among
my wireless router, client bridge, PC, and media extender.
Is there any value in using Cat6 ethernet cables with these devices? I
am using 802.11g and I might upgrade to 802.11n. I am interested in
performance, and also reliability. If a fancy cable can eliminate an
entry in a list of trouble-shooting tasks, I am all for it.
I also have Cat5 and Cat5e cables in my hell box. I don't really understand
the practical differences among all of these. I see that they are rated
to a maximum count of MHz, but I don't know how to translate that into
network performance and reliability.