Transistor level convertor
I need to build fast level converter, 5V in -&gt; 12V out ...
I have 100-1000pf load and need some 15-100ns fronts.

Both those requirements sound like MOSFET drivers. It's going to be extremely hard (not out of the question, but difficult) to do this with discrete transistors. If I had your requirements I'd look at low-side MOSFET drivers like the MIC4426 or FAN3111E.