Intel Core i7 5960X ES - Max frequency 2.805MHz?

I CAN'T answer re the "ES" version, but there's no 5960X ES version showing on intel's ark page - here's link to the 5960X spec page, you can use the "search" box at the top to search for the ES version and see for yourself

but if you download the Intel Extreme Tuning utility https://downloadcenter.intel.com/download/24075/Intel-Extreme-Tuning-Utility-Intel-XTU- you can install it and run the benchmark test
once it's run, whatever the score it will also display the clock speed your CPU demonstrated. There'll be a small button in green that appears, once you've run the benchmark test, suggesting you compare your score to others, clik on it, and it will upload your score as well as your settings (bios etc). Then minimize the tuning utility, and you should have a browser open to the HWBOT web - in the center select "ANALYSE" - when it goes to that page, at the top you can select your cpu as well as your mobo. It will then display on the chart a number of users test results.

On that chart or graph of small dots, if you hover your mouse over each one (your test result dot will already be highlighted by a red arrow) - but as you hover your mouse over the other dots, you'll see their score as well as percentage of compatibility for the settings ie 80%, 88% or 100%, as well as display what clock speed their cpu was hitting. DO not bother with any showing a higher clock speed at this point, but find one showing 3.0 to 3.5, with 100% compatibility, and clik on it. Then on the right hand side in the column, you'll see the specs for that cpu. At the top of that column on the right, you can download the settings that user had on his board. Download to your desktop,
then in the tuning utility, if you go to the "Profiles" (upper left column of choices, open it in full screen and clik on "import" and import those settings - you can then choose to apply those settings. If it shows a small box below "Apply" that says "force reboot", check that box.

then when those settings have been installed and system reboots, run the benchmark test again, and see if you clock speed has improved.

I'm getting ready to order that very CPU so i'll be curious what you find - hope this helps

forgot - here's a youtube video explaining the intel Extreme Tuning Utility https://www.youtube.com/watch?v=yFOwslwebC0

Note that "ES" versions are engineering samples.
They are usually send out before the actual market placement begins, tend to be unlocked.
See it as a very rare "beta version" of the CPU.

Keep that chip alive, you might sell it later for a really good price. even quite some years from now.
Just recently I saw a i7-4960X ES used for 500€ and 2 Xeon E5-2658 ES for 300€ on ebay.