One thing many Weblogic/Websphere people will agree upon - is to try and never install SSL encoding directly on the weblogic/websphere servers. Thats the quickest way to dramatically reduce the scalability of your WLS/WAS server and cause a lot of performance issues ! Theres a number of whitepapers out on the interwebs that talk about how Offloading SSL using a separate loadbalancer is the ideal way to deliver SSL to the end user, but keep the WAS/WLS servers scalable.
All loadbalancing options that you consider (F5/Netscaler or even Zen Loadbalancer) has the option to offload SSL - ie, from the end user to the loadbalancer, the traffic is delivered via https - but the loadbalancer deals with the certificate, and the "back-end" traffic (usually only contained within the datacenter on the same segment) is then delivered between the web server and the loadbalancer with http. Fast, scalable and reliable. And, in the case where there are a LOT of webservers, a reduced number of locations where SSL Keys have to be stored.
Consider offloading SSL in your architecture.