<9.Nxe5?! is also doubtful but worth looking at in a little more detail. After 9..c5! 10.Be3 (10.d5 Nxe4 11.Nxe4 Bxe5 is good for Black) there is:
1) 10..cxd4 11.Bxd4 and now:
1a) Several commentators give 11..Ng4 an '!', quoting the game Bystriakova-Umanskaya, Stavropol 1989, where Black had good positional compensation for the pawn after 12.Nf3 Bxd4 13.Qxd4 Nb4 14.0-0-0 Qxd4 15.Rxd4 Nc6 16.Rd2 Kg7 17.h3 Nf6 18.Re1 Be6.
1b) Whilst this seems OK for Black, I don't see any real necessity to head for an ending a pawn down. One idea is 11..Nb4?!, but after 12.Bc5 Qa5 13.Bxf8 Bxf8 we have probably given up a bit much material for our beautiful position.
1c) Perhaps the best line of all is 11..Qe7! as 12.0-0 Rd8 looks extremely awkward for White.
2) 10..Ng4!? occurred to me after seeing variation '1a' above. Although it is playable, it is no more effective than 10..cxd4. I have examined:
2a) 11.Bxg4 Bxg4 (you may wish to amuse yourself with 11..cxd4) 12.Nxg4 (12.Qxg4 cxd4 13.Bg5 Qa5) 12..cxd4 13.Nh6+ Kh8 14.0-0 f5! with good play for Black.
2b) 11.Nxg4 cxd4 (11..Bxg4 12.d5!) 12.Nh6+ Kh8 (12..Bxh6 13.Bxh6 Qh4+ would be fine for Black but White should play 13.Bxd4! with the advantage) 13.Bf2! Be6 14.Nd5 Qa5+ 15.Kf1 Bxh6 16.Bxd4+ Bg7 17.Bxg7+ Kxg7 18.Qd4+ f6 19.Kf2 Nb4! with adequate compensation for the pawn.>