Well, I think I have a winner 🙂
I played some more with Manga studio. I tested default brushes and it behaves very similarly to SAI which was my favorite before, Work with large files is ok. Masking layers and groups are also there. And since it offers much more flexible brush managment and few other features that might be useful, the decision is quite simple. Manga studio 5 seems to me like a really strong painting alternative to PS
I wanted to do full artwork like I did with all other programs(Astrid and Charly in sketchbook, Ostrich in PS(finished in SAI since it started to lag hard), Rooster rider and Poe were done in SAI), but as I said, demo does not have save, so hopefully there will not be some fatal flaw I do not see now 🙂