In previous log I've posted an idea - how to improve current->field transformation efficiency via something except of a good core material. So I experimented with that for a while and it seems to work.

So, what I've got for now:

1. Program
First of all - I've wrote a code, which calculates magnetic field in a core, corresponding to shape of a wire.
Because most of calculators have no idea about shape and it's crucial in that case : )
Also, thanks to Florian Festi, who shared a nice way how to think about coils, you can check it in comments under previous update, it's really very helpful!

Results (coil performance, one layer, same voltage, different wire diameter):
That is very interesting here - how better distribution of area (through which current flows) in case of small wire diameter increases efficiency drastically. Overall, wire is closer to the core and it almost reduces effect of current drop, in case of supplying with the same voltage:
75% current drop leads only to 35% magnetic field drop!

It means, that by using greater voltages (like 100V except of 30V) we can achieve amazing performance even with a bad core material, in case of single-layer coil! Of course, there still a question about heat dissipation, however, all experiments shown, that this stuff not likely to be heating much with such amazing control method, ahaha :)

And of course I experimented with that a lot, experiments show almost similar results.

2. Electromagnet design
Of course, I'm on my way to build one of this magnets. I made 18 cores (from nails this time, but who cares, if it would work with bad core material, it should do it best with nice pure-Fe cores later, obviously)

So now I'm on stage of wire-winding. Here is final design comparing to previous one:

Looks kinda weird, because it is in-scale and new design is kind of smaller :)
I would upload hi-res render to the description, I really like that Sci-Fi look.

You can see there improved stripe-fixation mechanism as well, which I described in previous updates

3. Control circuit's new version PCBs!
Yeah, I've received them today! Update about them - coming soon
In two days, I'm not sure what I would have time to solder tomorrow

I want to test them very much, they are kinda pretty, huhuhu