I'm trying to learn the basics of the Blumenfeld myself now and using the following sources:
- Two videos in the
"Alterman's Gambit Guide" series on
www.chess.fm.
-
SOS (Secrets of Opening Surprises) Vol. 11 article by Rogozenko on the accepted wirh 6...a6!?.
- Article by Chris Ward in
"Dangerous Weapons. The Benoni and Benko" outlining his own black repertoire in the Blumenfeld accepted.
I also have the aforementioned
Przewoznik book for reference. Actually there are two versions of it; one English-language by "Przewoznik and Pein" and one German-language by "Przewoznik and Konikowski", both from ca. 1991! I have the german version, but I have no idea how much difference there is between them (if any).
So far my impression is that Black has a wide choice of move orders in the accepted, and should be able to find something playable against each of White's lines there. Really critical is 6...d5 7.Nc3! and now Ward's 7...Bb7 8.e4 d4 9.e5 Nfd7 looks like the best try. Black is willing to sacrifice another pawn, allowing Bc4xe6+, for a lead in development and open lines for attack. If that ultimately fails I will look more closesly at Rogozenko's 6...a6 7.bxa6 Be7!?, though here 7...d5 8.Nc3 is also supposed to be less effective for White: 8...d4 9.Na4 Rxa6 10.Bd2 (10.b3 c4) 10...Ne4 11.e3 Nxd2 12.Nxd2 dxe3 "and White must give back the extra pawn, fighting for equality" -Rogozenko (13.fxe3 Qh4+ 14.g3 Qxa4).
Against 4.Bg5 there are a couple of White repertoire books that are useful to check: Palliser's
"Play 1.d4!" and Grivas'
"Beating the Fianchetto Defences" both recommend it. There's also an article in
SOS-10 that I haven't seen;
EDIT turns out this is about 5.Bg5 b4 which means I should get it ASAP! So far I'm looking at 5.Bg5 exd5 6.cxd5 d6 and 5.Bg5 b4!? and trying to make one of them work.
The "Dangerous Weapons" book also has a chapter on the related "Pseudo-Blumenfeld Gambit" 1.d4 Nf6 2.Nf3 c5 3.d5 e6 4.Nc3 b5!?, written by Richard Palliser.