I'm thinking of a Cross-Stack EtherChannel, but is it better to have one EtherChannel with 4 ports, or 2 EtherChannels with 2 ports each?
I would recommend one of 4 ports. Why? One logical link rather than two.
What would be the best way of configuring the links between the two stacks?
Two ports on each stack member for the stack of two. For the stack of three, either two ports on one stack member and one each on the other stack members, or two ports on two of the stack members.
On the Cisco site it states that a GigaBit EtherChannel can provide 8 Gb/s. Does this vary depending on how many ports are assigned to the channel?
As Mark mentions, some later devices support more. Originally, though, EtherChannel was limited to 8 links.
Yes, maximum bandwidth depends on links assigned.
There are other "gotchas". Such as: any one flow will only use one link. EtherChannel hashes flows across links regardless of current link usage. Flow distribution depends on the nature of your frames/packets and the hash algorithm being used. EtherChannel usually hashes best across a power of two number of links. If you need more than four EtherChannel links, you might investigate whether you would be better served by moving to the next jump in Ethernet bandwidth (if available).
