patzer2: <refutor> Thanks for the game and the recommendations from MCO on the Steinitz variation of the Scotch (4...Qh4).
In the 5. Nb5 Qxe4+ response, BCO gives 5...Qxe4+ 6. Be2 [if 6. Be3, then BCO gives 6...Qe5! 7. Nd2 d5 8. Nf3 Qe7 9. Qxd5 Be6 (O'Hanlon-Mikenas, Buenos Aires Ol 1939) 10. Qd2 Rd8 11. Bd3 Nb4 with a slight black advantage] 6...Kd8 [if 6...Bb4+, then 7. Be2 leads to a white advantage] 7. 0-0 a6 8. N1c3 Qe8 9. Nd4 as equality with compensation leaning towards a clear white advantage. One nice win I particularly enjoyed in this BCO recommended variation with 5...Qxe4+ 6. Be2 was Hebert vs Biyiasis, 1978
In the MCO main line you cite, BCO relegates their recommended 5. Nc3 to a footnote in favor of 5. Nb5! (exclamation point being Kasparov and Keene's in BCO). Their line here is 5. Nc3 Bb4 6. Ndb5 Qxe4+ 7. Be2 Bxc3+ 8. Nxc3 Qd4 (consider 8...Qe7!? intending 9. Nb5 Qd8) 9. Bd3 Nb4 10. 0-0! Nxd3 11. Nb5 Qc4 12. Qxd3 Qxd3 13. cd Kd8 14. Bf4 d6 15. Rac1 Bd7 16. Nxc7 Rc8 with equality.
However, as a very good option I do like the possibilities in the MCO recommendation 5. Nc3 Bb4 6. Be2! (exclamation point being MCO's I assume) with white winning 11 of 17 games in the Chessgames.com database (63.6%) and drawing two games (18.2%). Some wins showing white's potential in this sequence are Karjakin vs V Malinin, 2002 and S Kalevic vs A Dimovska, 2001 and S Prudnikova vs J Bokan, 2001 and D Petrukhin vs V Rudkovsky, 2001 and Z Vukovic vs Mozetic, 1991 and Oral vs M Kantorik, 2000
However, following this MCO recommendation resulted in a win for black in Z Medvegy vs A Karpatchev, 2001 and G Kjartansson vs O Simonsen, 2001 making me somewhat reluctant to enter this MCO recommended variation. Also holding a U.S. GM to the better of a draw in Ashley vs D Bokan, 1998 as well as the draw secured in R Espinoza vs L Day, 1994 seems to indicate black has more than adequate defensive resources in this line.
I suppose if I had to enter the Stenitz as White I am currently leaning toward the reply 5. Nb5 (Kasparov and Keene's main recommendation in BCO) or 5. Qd3 (recommended as leading to a slight white advantage by Kasparov and Keene in BCO) as in
Maczuski vs Kolisch, 1864 (where you will find more discussion of the 4...Qh4 line along with a post giving information on two books on the line by GM Gutman and IM Hall respectively).
However, note that I enjoy games with tactics and complicated positions, so more positional players who like more clarity and certainty might prefer the MCO recommendation 5. Nc3 Bb4 6. Be2! However, tactically inclined players might find more fireworks and double edged play with 5. Nb5.