APC, Memcache, and xcache

[Kaelon]

Hi Everyone,


I have a "big board" (30,000 active users, 1.3 million posts, around 500 concurrent users at normal peaks), but never used (or know much about) PHP Accelerators / Caches. In a recent conversation over at vB.com, it was suggested that future versions of vBulletin will make great use of APC and Memcache. So I installed both APC and Memcache, and I set the config.php Datastore to APC.

1. Can I use both APC and Memcache? Does this make sense?
2. I have heard a lot of talk about xcache. Is this preferrable to either or both?
3. How can I make sure that vBulletin is using APC, Memcache, and/or xcache?

Thanks!

Edit: This particular site is running on a single Enterprise Intel Quad Core Xeon Server.