Single or dual 4500e for redundancy

Question

I apologize if this has been asked before, but I haven't been able to find a solid answer when searching.
We're deploying a new datacenter and will have 20 racks of servers, mostly 1u.  Given our bandwidth needs which are reasonably modest we're planning on using dual 2960s switches at the top of the racks and aggregating on a single or dual 4500e using 10gig links.  The 4500e(s) will also have a bunch of 1gb devices such as firewalls, routers, and load balancers connected to them.  Pretty typical network core.    Given the need for 40 10gb links to racks and then another 20-or-so 1gb, the 4500e chassis seems to fit the bill.
My question is, do we go with a single 4507e with full redundancy (dual 10gb cards, one link to each from each rack, dual 1gb card, and dual supervisors) or a pair of either 4506e switches each with their own cards.  With a virtual chassis the 4506e is appealing, but I'm not up to speed on any limitations that might impose.   With IISU and the like does having two physical chassis vs everything in a single actually buy us anything if they're going to be in the same physical proximity anyway?  A big reason to go with the single chassis is space - 11 rack units vs 20.
If we do go with a single chasis, other than Cisco's HA docs on the 4500e, is there any documentation or case studies that I could use to sell the idea to management?  A number of people, especiailly those in favor of a ton of cheap netgear switches, argue that a single chassis is a single point of failure and we should never do it.
Thanks!

Answer 1

Disclaimer
The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.
Liability Disclaimer
In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.
Posting
As you've described, the problem with any single chassis, the chassis itself can become a single point of failure even when loaded with redundant components.  Independent chassis (e.g. VSS, StackWise) provide chassis redundancy although it does raise a question on software redundancy, i.e. multiple chassis are running some form of tightly coupled chassis OS vs. standalone chassis.  Standalone chassis should be, in theory, the most redundant but they too create issues such as load sharing and asymmetrical path issues (e.g. unicast flooding).  If you understand and trust a multi-chassis OS, I personally think it's often the "better" redundancy option.
I don't know if VSS on the 4500s support it, but 6500 VSS supports quad supervisiors, so if you lose a single sup on those you don't lose one of your VSS chassis pair.
Regarding your later post on using a 4500-X VSS pair, yes that might be an idea core for high density 10g.  For twenty 10g ports each, you would need either the 16 port with the optional 8 port module or the 32 port model.
Depending on your remote rack setups, you might also consider 3750-Xs, stacked, in lieu of multiple (individual cabinet) ToR 2960S pairs.  StackWisePlus is a much better stacking technology then FlexStack.  Yes, the 3750-Xs are more expensive, but you might need less if you can bring multiple racks to the same 3750-X stack.  (Depending on how many downstream stacks you actually need, you might also reduce your need for 10g ports on the core.)  Depending on your feature needs, you might even be able to use the LAN Base models which in the later IOSs also support StackPower.
10g is nice, but it's also expensive.  When working with switches within 100m, don't overlook the possibilities of gig copper Etherchannels.  For example compare total cost of 8xgig (copper) build-in ports vs. single 10g (fiber) especially if special module is required.