Mac Pro memory prices have dropped a bit more for 8GB modules, which means that for the first time, you can now get 64GB of memory for your 8-core or 12-core Mac Pro for under $1500.
That said, if 48GB is enough, it is to be preferred, because 6 modules offer greater memory bandwidth than 8 modules, and in the 4/6-core Mac Pro, 3 modules are faster than 4. The effect is small, but measurable.
With memory, enough is enough. When 48GB is ample, 64GB won’t help. But when 48GB is not quite enough, 64GB can be much faster (ditto for 24/32GB in 4/6-core Mac Pros).
Apple memory remains expensive, for more on that topic, see my Jan 28 entry.
Prices for iMac and MacBook Pro are also very low (excepting the very latest 12GB and 16GB technology for the MacBook Pro).