Thanks for your reply, pjiang.
I was also told that if unfortunately I get RFE, then nobody knows how long it will take even for premium processing.
Anyway, I think most likely I'll go for H1B first while in the meantime I'll prepare documents for O visa. In this way maybe it will take a little bit longer time, but less risky and I'll also have a little more time to prepare.
Thanks again for your reply.