Just to throw one more datapoint in the mix - I had a pair of 7240 locals running around 1200 APs. On 6.4 code, they were around 40% to 50% memory utilization.
After upgrading to 8.1, though, they shot up to > 90%. I took immediate advantage of the trade in/upgrade option, and the additional memory in the XM model put me back under 50% again.