I did convert mtb to SS once then gave it to friend.
In case of fixie it had to be frame with horizontal dropouts.

That is not entirely true. You can go fixed without horizontal dropouts. EBB or if you are feeling up to the task, figuring out the magic ratio.

or chain with half-link

Or White Industries ENO (eccentric hub).

Correct me if I'm wrong, but don't track frames have a higher bottom bracket? If so, then yes, a smaller size is preferable. No one has mentioned this yet, so I figured it was much like sizing a MTB.

Bottom bracket height has almost nothing to do with what size frame a rider needs.

Yeah, I guess 2 cm is almost nothing.

It only affects standover, which has no impact on fitup on the bike.

assuming that:
56cm frame is for 5′ 10″ - 6′ 1″ height
58cm frame is for 6′ 0″ - 6′ 2″ height

being 6′ 0″ tall I bought 56cm frame (old racing bike built on 531st tubes)
I quickly measured front wheel - bottom bracket, just 1cm shorter than my old 58cm bike so there should be no toe overlap.
stem to be replaced by short steep one.
thinking about the bar.

Hey, you all can do whatever you want. Personally, I won't buy a bike that I can't stand over. And I really wouldn't want to be doing a trick and need to put a foot down and injure myself in a sensitive area. Just saying.

there are frames with horizontal and sloping top tube.

Thanks to everyone for the replies.
This is the frame I bought:
https://flic.kr/p/TNnNSh