We are deploying a new set of VMware server farms and would like to use the Nexus line for these 40 servers. Does is make sense to connect these via layer 2 to our VSS on a WS-X6708-10G-3C? Or should we wait a few years until we have a budget for a pair of Nexus 7k's and run everything to the VSS? thanks
Nexus 5000 is a L2 switch, so pretty much whatever you do, its going to be a L2 Portchannel 'northbound' from N5K up to the C6K VSS pair.
Your VSS pair would be the L2/L3 boundary, so you'd have a SVI configured on it that is the L3 default gateway (from your servers).
Best practice would be that you distribute the portchannel members across the pair of physical switches in the VSS pair.
I'm involved in the development of the Nexus range within Cisco, so I'd be all for recommending you deploy Nexus 7000 too. :) But the reality is that you can probably achieve what you want today with C6K VSS, and in future if you did deploy Nexus 7000 too, you could make use of virtual Port Channel (vPC) to allow for full bisectional bandwidth from 'access' to 'agg/core' without any blocked links in STP.
vPC is available today on N7K and provides roughly similar L2 multichassis etherchannel as what VSS enables today in C6K VSS.
hope that helps.