No, Einstein doesn't support DPFP, so performance there is not so great. To give you an example, 2 concurrent BRP6 tasks take 13k seconds on the Tesla, while on a 660 Ti it takes 18k sec. So not even twice as fast.
The only DPFP load I tried yet is Milkyway and I posted some results in the thread at XS: http://www.xtremesystems.org/forums/showthread.php?290290-New-toy-arrived
On screenshots posted there you can see the temperatures and power, I think the one was made while running E@H. I need to update it, since HWiNFO wasn't showing Tesla's parameters, which I fixed yesterday.

As for temperatures, in Fan Auto mode I get ~70 and ~50 C on those 105 W CPUs.
I am somehow disappointed with the fan Auto Mode, because it seems to favor noise over temperatures quite much. So on the T7610 (with 2x150W CPUs) the temperatures can easily climb to 80-90 C. I'm discussing this with DELL and hoping for a BIOS update...

As for ES CPUs this is very different for each CPU generation / model.
Basically Engineering Sample CPUs are those produced by Intel during final validation phases and sent to OEM/ODMs/etc for board bring-up and various validation purposes (boot, OS, thermal characteristics, performance testing, etc).
There are several stages during this process: ES0, ES1, ES2, QS, and sometimes even more. The more mature the stage is, the less critical errata are present. So in most cases QS parts are almost production quality.
But everything depends on particular CPU model and ES stage. There's no general rule that ESn won't have a certain feature and will have a certain amount of critical/non-critical bugs.
Some CPUs made it very well during the early stages, some others need more steppings and updates..

Also another thing is that ES CPUs are property of Intel and not for sale.
When checking those parts, you should verify the QDF numbers. But I think the ES database is not for public.

My experience of B1 cpu's combined with WCG has been all good. I have not used them for anything else however.

The very nature of these e5 processors is that they run in dual cpu MB's

When these were first becoming available at the time when the retail cpu's were launched, the most commonly mentioned boards used for testing were thw Asus Z9PE D8 WS and the Supermicro X9-DAi. The point mentioned by most sellers was that these will only work with early bioses.... certainly not with anything later than those first v2 bios offerings. If you have a particular MB in mind the ask the seller if he considers that to be compatible.

If you need to change the bios version then a single secondhand retail e5-2603 is possibly the way to run any duallie MB for this purpose.

in the greater scheme of things the order of older to newer es cpu's is: B0, B1, .......C1 maybe C2 then retail although there are some oddballs like M1 (see Mumak's post above}

In my particular case my e5-26xx cpu's run at 2.3 but only get 2,4 at turbo fully loaded so are harder to call on the actual model number. These appear to be the same from the hardware info page photo.

I consider the maximum fully loaded speed to be the important one so for me these are e5-2650's even though they were sold as 2665's

http://www.cpu-world.com/sspec/QA/QAMU.html#related

then the C1 through to production is

http://www.cpu-world.com/CPUs/Xeon/Intel-Xeon%20E5-2660.html

EDIT:

Should you decide to buy these and find you cannot run them in your chosen MB then contact me and I will be happy to buy them from you as I believe I already have a board.

Yep, I think it is the cheapest. It must be a retail cpu to be supported by ALL bios's. You might be well advised to check on the availability of early bioses.

Added a few edits above.