Switched 1600 micro steps, so that's 320 steps per mm. Maximum speed I could achieve smooth and without stalling was 3000 mm/s with 750 accu for all axis, seems good enough for milling aluminium.
Now I have to tie all the wires down properly, get the Y in 90* in respect to X and tie the bolts down... Most importantly, I have to get familiar with Mach3 software which I guess will take a while. Limit switches are on their way, pity that FVD doesn't work, but hey, positive thinking? :D
Thanks all of you, I wouldn't have managed this far if not because of this forum, that's for sure. I added short video filmed from phone (sorry for quality), I will have proper topic with all the build process and photos/videos in few weeks.