Suitable openings against d4

IQPs give you active pieces and squares for those active pieces - in the first IQP tarrasch position with Ne4 all of the pieces have practically been traded except rooks and queens, which is the best theoretical possibility for the side playing against the isolated pawn. In the second one with Nd5, it is white with the active pieces, so in both black is clearly worse. Also, it goes against principle to accept an isolated queen pawn as black, where you don't have development to compensate the loss. I have nothing against IQPs, and frequently get them in certain variations of the QGA, but I don't believe that the Tarrasch is a good opening for black.

sdf

It's not the best opening in the universe, the Hennig-Schara, but because it is so wide open and Black has initiative, it is actually more difficult for White to hold his pawn lead from that position than you might think.

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From several positions after that, Black can force a trade of the light-squared bishop for the knight on f3, creating an isolated pawn and double-pawns which are sufficient compensation for Black's missing pawn (and for losing his bishop).

There are of course improvements for white on that line too I believe, as I played the entire line OTB in a 2 hour game, with no preparation against that gambit beforehand.

And I'm just as interested in the actual Tarrasch as the gambit. Here Akobian gets destroyed in 26 moves, which is one of the highest rated games I can find until I get my laptop restarted (my chessbase froze):

And this is the more complicated line - I believe Ne4 instead leads to a simpler edge.

suitable for what?

I don't even remember the OP at this point - so I can't anwer that - this thread is like a year old and somehow got revived.