Stay with Nimble and order 440 with 2TB cache. Make this storage only for VDI like us. We have Nimble for the servers and Nimble for VDI. Same for the redundant site as well. Nimble release 2.0 code and now you can bundle 2 storages together to share resources. I went to our vcenter, select 250 desktop and reset them. They reboot and the storage went to 160K IOPs. No sweat for the storage. Couple of minutes later all desktops were up like nothing happen. Their support is excellent. You want to have working VDI here is the recipe:
2 UCS chassis with 8 B230 M2 20 CPU cores and 512GB memory in.
Nimble CS440G-X4
EVGA zero client Tera2321 (latest one have 512MB memory) www.evga.com
VMware View 5.3 with remote experience enabled.
All this is 10GB network in the datacenter.
You will have 8 more slots for servers to grow, and with the current you can have 800 VDI easy if you allocate 4GB of memory per VDI. Add 8 more to it and you have 1600 VDI.
It is pricey in the beginning , but after that is just fun to sit and think where you will go fishing today 
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The installation will take 2-3 days at the most. I did the install many times.