EmployeeRe: performance
I have not done any performance comparison.
Re: iRule for enable client/server ssl profile
You can only select a server ssl profile from a Local Traffic Policy. IMHO it makes sense to use a Local Traffic Policy as "tier 1" that uses VIP targeting (via the policy) to multiple different virtual servers that have different clientssl profile attached.
Alternately, you could set a variable in the local traffic policy and later use an iRule (attached to the same virtual server as the local traffic policy) to assign the clientssl profile via SSL::profile (I have not tried this, seems plausible).
not sure if that answers your question.
Re: why ssl persistence
My best guess is that it exposes variables that are necessary by Local Traffic Policy. For example if you try to invoke an iRule that acts on the CLIENTSSL_CLIENTHELLO event you will get the following error
01071912:3: CLIENTSSL_CLIENTHELLO event in rule (/Common/test_sni) requires an associated CLIENTSSL or PERSIST profile on the virtual-server (/Common/test_sni).
Re: ssl persistence on pool
If you are sending traffic to a pool you may want to have a combination of ssl persistence and source ip persistence. otherwise you could see an issue where a client will renegotiate the ssl session. this could occur when reconnecting and getting sent to a different backend server.
agree that the behavior could be unwanted depending on the use-case. typically you want to preserve connections to the same backend for SSL connections.
Thanks for your feedback/questions!
Eric