Caching Panel page variants
Did you try any off the following module

Panels Page Cache


  This plugin can cache panels based on the path/url (arg() structure).
  
  This is needed if a panel has content which is dynamically per page
  (eg ad-tags, content related items).


Panels Hash Cache


  This module provides a hash-based cache for Panels and other Chaos
  Tools powered displays.
  This support caching based on any combination of:

Contexts (node, term, user etc)
Arguments
Drupal Path (args) (same as the Panels Page Cache Module)
Full URL (including domain and query string)
Users
Roles