Up until recently we've had a pair of 7200 controllers with a VRRP address. As we're nearing the limit of one controller's ability to sustain our AP estate we've added another two controllers.
As of now, we're back to two live, rolled back to 6.4.2.4, and the second pair are running 6.4.2.6 with a small number of APs.
The controllers each have two 10Gbe ports trunked to our procurve switches.
All was working just fine on 6.4.2.4, and indeed the original pair of controllers are now fine on that code with about 1897 APs.
The APs we moved over to the test controllers running 6.4.2.6 all rebootstrapped over the weekend, so it isn't load dependent. When the problem occurs we lose all APs on the affected controller.