We have 9000 nodes, 50 groups, 250 users, 5 roles. Roles are Content Writer, Content Editor, Content Manager, SiteBuilders, Administrators. Published page response is really fast 3s to 4s, but when editing it takes more than 4 mins for mentioned roles except administrators. I am clueless where to start optimization. We have memcache, mysql query cache enabled, advagg module enabled. We have OG module, Workbench Module, CPN, Metatag. Apache eats CPU 90 to 100%, memcache eats 34% memory. Please help me.

Query log for content writer role:
Executed 60799 queries in 10842.7 ms. Queries exceeding 50 ms are highlighted. Page execution time was 63589.95 ms. Memory used at: devel_boot()=2.56 MB, devel_shutdown()=324.47 MB, PHP peak=51