[j-nsp] QFX vs EX4550 as collapsed core

[Andy Litzinger]

Hi,
we're deploying to a new environment where there will be about 500 virtual servers hosted completely on Cisco UCS.  The Core would mostly be hosting uplinks to the UCS Fabric Interconnects (End Host Mode), inter-vlan routing and links to service appliances (FW/LB) and the Internet edge routers.  Nearly all of our traffic is North/South from server to LB to internet or server to LB to another server.  The core would mostly be routing a few (dozens at most) routes so RIB/FIB size shouldn't be a great concern.  Most links will be 10G, but there are a handful of 1G management links.

We're considering either the QFX3500 ( x2) or the EX4450 (x2 as a VC) to fill this role (or potentially Cisco Nexus 6001)

* are there any L3 benefits of one over the other?  I haven't found clear numbers in the datasheets
* Has anyone actually used MC-LAG on the QFX3500?  Is it working well? any caveats?

we've also considered collapsing the edge too, but the cost of say an MX-480 with similar port count is about twice that of an MX-80 + QFX/EX

thanks!
-andy