It's tough. You just have to figure out if getting any of this gear at the moment makes sense for you. I agree with what mikey says below here. In this instance it could be worth it to pay a reseller their mark-up. It puts he gear in your hands sooner, so you don't slowly watch the Diff rise and kill your profits. Most hardware out has already sold a Batch a month starting Aug/Sep leading all the way to November. This means a potential Diff increase similar to the beginning of 2018.
The difference there was that there was a lot of gear available on hand. So people paid absurd prices based on the market and then watched each batch boost the Diff. Obviously as price tanked so did a lot of the hashrate. Hard to say what Diff will look like in December but if this price continues to hold, and all gear sold ships out we might be sitting 30% higher than we are now.
another option would be buying whatever is available now or has less waiting time, saw someone on Telegram selling M21s-56th (End of July) for about 3200$ and S17 4000$ (Aug) in china.
In the meantime you can check this thread out and see all new gear then check to see what you want, and when it might be available.
Current List of Competitive Hardware - July 2019
