Sloughterchess has given a nasty move which I did not cover, yet it has just blown a hole in variation B.
7.Bxc6 dxc6 8.Nf3!
I am proceeding to find an answer to this simple move.
5.Bxf7+, 6.Bd5
Sort:
Okay, I think I have found a way for black against 8.Nf3.
1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5 5.Bxf7+ Ke7 6.Bd5 Rf8 7.Bxc6 dxc6 8.Nf3 Nxe4!
I think this move is critical otherwise black is losing a lot of time playing a move like 8...Kf7.
9.Qe2 Nxf2 10.Rf1 Qd6! this is the only move that holds. Two tries by white.
11.d3 Ng4?
This move comes very close to working. Unfortunately it is refuted by:
12.Nc3! Be6 13.Ne4 Qd5 14.Bd2 b5 15.0-0-0 Bd6 16.Nc3 Qc5 17.h3 Nf6 18.Be3 Qb4 19.a3 Qa5 20.Bd4!! b4 21.Nxe5 Qa6 22.axb4 and black is in trouble.
A better try is
11...Bg4 12.Bg5+ Kd7! and black is all right.
13.Rxf2 Bxf2+ 14.Qxf2 Bxf3 15.gxf3 Rf5 16.Be3 Qb4+ 17.c3 Qb5 18.c4 Qa5+ 19.Qd2 Qxd2+ 20.Nxd2 Rh5 21.Bg1 Rd8 22.Ne4 b6 and I think the position is equal as white has adequate compensation for black's extra pawn.
White tried to improve with 11.Nc3
11.Nc3 Bg4 12.Rxf2 Bxf2+ 13.Qxf2 Bxf3 14.gxf3 Qf6 15.b3 Kd7 16.Ba3 Rf7 17.0-0-0 Qxf3 18.Qh4 h6 and black is looking good in the endgame.
This is certainly a rough variation for black if he is not prepared. There are probably improvements available, but black should only put hope in 8...Nxe4 unless 8...Kf7 is shown to be good. I think with best play black can hold.
5.Bxf7+ Ke7 6.Bd5 Rf8 7.Bxc6 bxc6 8.Nf3 Nxe4? is refuted by 9.Qe2 Nxf2 10.Rf1 Qd6 11.d4!
Looks like it is time to go back to the drawing board.
I think that 5.Bxf7+ Ke7 6.Bd5 d6!? should be looked at now as a possibility to avoid these problem lines.
8...Bg4 is the best move objectively, but does not gain full compensation for the pawn.
5.Bxf7+ Ke7 6.Bd5 Rf8 7.Bxc6 bxc6 8.Nf3 Bg4 9.d3 Qe8 10.Be3 Bxe3 11.fxe3 and white has a slight advantage.
This section deals with with the variation after 5.Bxf7+ Ke7 6.Bd5.
The current status is that black is fine in this variation. White can choose between the complicated 7.0-0 or the easier 7.Bxc6. The 7.0-0 variation is extremely complex and it is not clear in some lines whether either side has an advantage. Black should have enough compensation for equality with best play. White should look at variation A3.
5.Bxf7+ Ke7 6.Bd5 Rf8
Best move for black by test; threatens Bxf2+. Two ways to play for white.
A: 7.0-0 d6
Now white has four moves:
A1: 8.c3 Bg4 and white has three queen moves:
9.Qa4 Qe8 10.Bxc6 Qxc6 11.Qxc6 bxc6 and black is better
9.Qb3 Bb6 10.Bxc6 (10.h3 h6 11.d4 (11.Nf7 Qd7 12.hxg4 Qxg4) 11...hxg5 12.hxg4 Qe8) 10...bxc6 11.h3 h6 12.hxg4 hxg5 13.d4 Qe8
9.Qe1 h6 10.d4 Bb6 11.h3 hxg5 12.hxg4 Qd7 13.Na3 (13.Bxg5? Qxg4 14.Bxf6+ Rxf6 and black has a huge initiative) 13...Qxg4 14.f3 Qh5 15.Nc4 g4 16.Nxb6 axb6 17.Qg3 exd4 18.Bxc6 bxc6 19.cxd4 gxf3 20.gxf3 g5 21.e5 Nh7 22.Kg2 Rae8 23.Bd2 Qg6 24.Rae1 Kd8 25.Rh1 with a mess.
A2: 8.d3 Bg4 9.Qd2 (9.Nf3 Nd4! 10.Nbd2 (10.c3? Nxf3+ 11.gxf3 Bh3 12.Re1 Qe8 13.Qd2 Nxd5 14.exd5 Rxf3 15.Qg5+ Kd7 16.d4 Qf7 17.Be3 h6; 10.Bxb7? Rb8 11.Ba6 Qe8 12.Nbd2 Qg6 Kh1 Nd7) 10...Nxf3+ 11.Nxf3 Nxd5 12.exd5 Bxf3 13.gxf3 Kd7 14.Be3 Rf5 15.Bxc5 dxc5 16.Qe2 and black is better) 9...h6 10.h3 Bd7 11.Nf3 Qe8 12.Bxc6 bxc6 13.b4 Bb6 14.Nc3? (14.c4 Nxe4 15.dxe4 Rxf3 16.c5 dxc5 17.bxc5 Bxc5 18.Qa5 Bd4 19.Nd2 Rd3 20.Rb1 Qg6; 14.Qd1 Qg6 15.Kh1) 14...Nh5 15.Kh2? (15.Qd1) 15...Rxf3 16.gxf3 Nf4 17.Ne2 Qh5 18.Nxf4 exf4 19.Rh1 Bxh3 20.d4 Rf8
A3: 8.Bxc6 bxc6 9.Nf3 Kf7!? (9...Bg4 10.c3 Qe8 11.d4 exd4 12.cxd4 Bxf3 13.gxf3 Bb6 14.Kh1 and white has reasonable chances of consolidating) 10.d4 (10.c3 Kg8 11.d4 exd4 12.cxd4 Bb6) 10...exd4 11.Nxd4 Kg8 12.Qd3 Qe8 unclear
A4: 8.h3 Qe8 9.c3 (9.d3 Qg6 (9...h6!? 10.Nf3 Qh5 11.Bxc6 bxc6 12.Nc3 (12.Be3 Bxh3 13.gxh3 Nxe4 14.dxe4 (14.Nxe5 Qxe5 15.d4 Qf5 16.dxc5 Qxh3 17.cxd6+ Kd7 18.dxc7+ Kxc7 19.Nd2 Nxd2 20.Bxd2 Rf3 21.Ba5+ Kb7 22.Qd4 Rg3+ 23.fxg3 Qxg3+ leads to a draw) 14...Rxf3 15.Nd2 Raf8 16.Nxf3 Rxf3 17.Bxc5 dxc5 18.Re1 Qg6+ 19.Kf1 Rxh3 with perpetual check coming) 12...g5! and black has a strong attack) 10.Kh1 (10.Bxc6!?) 10...h6 11.Nf3 Nxd5! 12.exd5 Nb4 13.Nc3 Qh5 14.Ne1 (14.a3? Bg4 15.axb4 Bxf3 16.Qxf3 Rxf3 17.bxc5 Rf6 and black wins) 14...Qxd1 15.Nxd1 Nxd5 16.c4 Nf4 17.Nc3 Be6) 9...Qg6 10.d4 Bb6 11.f4 (11.Be3 Nh5 12.Qd2 Nf4 and black has a strong initiative) 11...exf4 12.Bxf4 h6 13.Nf3 Nxd5 14.exd5 Rxf4 15.dxc6 bxc6 and black is slightly better.
B: 7.Bxc6 dxc6 8.Qe2 (8.d3 Ng4 9.Nh3 Nxf2 10.Bg5+ Kd6! 11.Bxd8 (11.Qh5 Bg4 12.Qxh7 Qd7) 11...Nxd1 12.Bxc7+ Kxc7 13.Kxd1 Rf6 and black has a significant advantage) 8...Qe8 9.0-0 (9.d3 Qg6 10.Nf3 Nh5 with compensation) 9...Qg6 10.d3 Bg4 11.Qe1 h6 12.b4 Bd6 13.h3 Bh5 14.c4 Kd7 and black is better.