There some false information here. Unlocked multipliers are a total rarity in ES chips. almost all ES chips are exact counterparts or the future retail version. Extreme chips are unlocked, others are not. I have seen E6300s, E6400s, E6600s, E6700s, E8400s, E8500s, X6800s, QX6700s, QX6850s, QX9650s, LGA775 Xeons both Dual and Quads, and so on. I have never seen a non extreme chip with unlocked multipliers, with the exception of one E6400. Completely random.
Secondly OP, there are many kinds of ES chips:
There are very early steppings, which in the Core 2 family were denominated B0. These chips are the ones used for early demonstrations at IDF. They lack almost all features, such as EIST, C1E, TM1 and TM2. These can be easily recognized since in the microcode they are marked as Genuine Intel CPU (R), and there is no model. The only way to "call it" is by finding out what the default multiplier is. You want to stay away from these, they were never meant to be used 24/7.
After these come B1. These chips are usually sent out to motherboard manufacturers for testing purposes. These chips are usually fully functional. The microcode is also marked correctly. Some of these chips go to reviewers for very early press previews, and they get sold for insane prices since they are functional pre-retail chips.
After these come B2/B3. These chips are identical to their retail counterparts in every way. These chips are sent out to reviewers just before the NDA is lifted for press reviews. These are the most common chips being sold as engineering samples, since they end up in the hands of reviewers that have no scruples in making a few extra dollars.
Lastly G0 engineering samples, which are identical to retail parts, were handed out to motherboard manufacturers for compatibility testing.