This is an interesting set indeed. Because even after giving it a lot of thought, I'm still not certain whether to go engine or slog.
I can see two different lines with some variations.
Plan 1: focus on Silk Roads
1a - Open Silver/Cutpurse, then get horse traders, dip into Harems first
1b - Open Silver/Horse Traders, maybe harems maybe immediately silk roads
Plan 2: focus on Grand market
2a - Open Steward/Silver, trashing&labs simultaneous
2b - Open Steward/Steward, trash aggressively
2c - Open Steward/Feast, more focus on early labs
2d - double tact.
The easiest comment is that 2d is barely worth worth mentioning. DoubleTact really needs villages, or maybe Vault. Here you need Grand Markets as only source of virtual money, and you need real money to get them, which will be worthless after you start double tact. Even on a 5/2 its horrible, if you want to go for Grand Markets just open lab/- (almost as good as 4/3).
1b clearly defeats 1a in a silk road mirror, because of the +buy for winning the estate split after silk roads are gone. Oh and also for just being the better card in a green deck.
Looking at the variants under 2, I think 2c is my favorite. If your terminals clash you can just trash down and use the feast->lab later on. Not great but no real disaster either. 2b works remarkably well if you happen to draw the Silver and the Steward in the same hand, using turns 3/4 for a Silver, Warehouse and trashing. 2b is also quite good actually, a lot better then most people give it credit for. You don't need good $2 cards or even villages to make double steward shine. Most of all you need a board where trashing is really good (think Highway). But here I think it gets beaten by 2a/2c.
So the most interesting question is: what happens if one player (taking a wild guess: WanderingWinder) plays with 1b, where the other goes for 2a/b/c?
I think it's reasonably close here. And when it's close, I always go engine. After doing
a lot of single player I'd say you need around 14 turns to pick up all Grand Markets, if you don't need to deny Silk Roads before that and don't get attacked by the Cutpurse. After that your deck is super super powerful and you don't need much more then 3 turns to end it on provinces.
That still looks like a losing line, because all provinces won't be enough. By that time the silk road player will have all 8 silk roads, almost 11 estates and lets say 3 harems (eventually worth 8*5+11+6=57). Besides, the game would be over because the Silk Roads, Estates and Grand Markets are all gone.
The solution however is simple. Don't buy out the Grand markets (leave 1 or 2), and deny at least some Silk Roads. Preferably 3, but even with 2 you have a good shot at this. If you get only 2 the Silk Road player probably was forced to buy too many too early, thus seriously reducing his chances at Duchies/Harems/double estate turns. And you still have some double province turns to come, or you can eat any menu of harems/duchies/laboratories first if that looks better.