Is anybody still using legacy CPU corona version? If so, what 3dsmax versions? I am thinking of dropping legacy builds for daily builds, it seems only a small percentage of people actually have such old CPU...
With Intel Processors it's simple, considering barely any PC will have core 2 Quads from 2007 or earlier.
6-core Phenom IIs however were still in production in 2011, packed a punch and quite a view are still around.
We cannot possibly know how much of the user base uses these in old Servers and possible older render nodes, since no Benchmark from Corona supported legacy. In the a4 benchmark thread 5 posts asked about / commented on phenom support out of 38 pages, in the 1.3 Thread 1 post out of 10 pages.
You can safely assume, that your testing crowd won't cry for dropped support, as long as the proper releases will have the option. Besides, I presume you are flexible enough to build legacy upon request, if there happen to be daily users with Phenom II nodes requests.