6K is a suited as a distribution switch (aka distro). Basically all your FEX hook up to your 5K/6K and then these distro hook up to the 7K. You can hook up the FEX directly to the 7K but this would be expensive because if you go beyond that then you need to either get another 7K or 5K/6K.
6K is more suited for multiple 40 Gbps links from FEX. If your FEX has an uplink of only 1Gbps or 10 Gbps then you can also get the 5K even though the 6K can support both 10 Gbps and 40 Gbps.
If you have the funds, I would go with 6004 as a distro and 7000 or 7700 with Sup2e supervisor card and FAB-2 line cards. Don't even bother with the Supervisor1 card because Cisco could be announcing the Sup1 EoS sometime in August 2014. If you plan to get Nexus 7K, don't bother with F1 and M1 cards. Go with F2e and/or M2. If you go with 7700, then get the M2 with F3 cards.
As what Richard has asked, what are you planning to do and what can your budget allow you to do.
Introduction This article will help you understand the steps on how to
download the UCS licenses from the Cisco Systems website and then
installing it on the UCS. The redacted (blue lines) just covers up
certain numbers for privacy please do not take them...
Introduction This article will help you understand and educate the
customer on how to clear their "expired licenses"
(license-graceperiod-expired) from their UCS-M. If a customer just
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==================== VIC FNIC driver does not support Virtual Volumes (
second level LUN ID ) An enhancement request has been created to track
this feature - CSCux64473 UPDATE - 12-14-2016 We made some traction on
the enhancement request - The Fix is in t...