Wow, I hadn't considered B. A is implausible I believe because the German economy of 1914 was export based on chemicals and advanced technology and industry. Why war with Russia when you can sell them stuff?
B could lead to revolution in Russia even faster. Now instead of going to war to ostensibly protect Serbia, soldiers are suffering and dying and seeing their friends blown apart to satisfy the greed of French banks. And on top of that, against the wishes of the Tsar. Not good for morale or stability.
Normally A is, curiously, the only time when the "economic logic" you described ("Why go to war with them when I can sell them things?") doesn't apply.
Instead, two other assumptions are applied as usual here in the forum:
Either it's A2 ("We have to go to war against Russia to shut down their economy before they overtake us in 10 years and crush us, please ignore that these are just purely speculative projections made by people who have a vested interest in going to war against Russia for the reasons described in point A3").
Either it's A3 ("British propaganda about how Imperial Germany are 'Huns' and Nazis in Imperial uniforms is 100% true. So naturally they would go to war of aggression against Russia 'because we can, because they exist and are racially inferior ' because that's exactly what the Huns do."
As for B, yes, that would probably lead to an even faster revolution. But interestingly this could even be better for Russia, in the sense that the republican government could be quickly consolidated.
Since the only reason the Russians have gone to war is because the pro-France faction has overthrown (and surely assassinated) the Tsar, none of the revolutionaries would feel that "I need to continue the war to build credibility with the Entente"...
....because from their point of view the Entente first burned all bridges by promoting a coup and dragging Russia into the war against its will.
Given that the signals sent by Russia are that the new government is purging the pro-Entente faction as traitors to Russia and wants peace, it is likely that the Germans will even decide to suspend the operation "send Lenin to Russia"...
And This is assuming, of course, that the Entente doesn't decide to have another even bigger brain fart and order an Allied intervention in Russia...
...to install a puppet government and force the Russian Republic to continue the war against Germany.