On the assumption you could get a 1080 for 450, i'd agree

But can you?

That's what I paid for my one and only 1080

i don't think you've done the math

Obviously I am a noobie member, so take what I say with a grain of salt.  

 I think its obvious that these machines will not make the returns that the mining calculators are spitting out, for reasons that have already been stated in this thread and many others.  That being said, no one knows exactly what will happen with price or difficulty increase rate.  

Personally, I ordered eight L3 machines this month, and I plan on selling four of them at double what I paid for them on amazon or ebay.   This means I will get 4 free machines, with instant ROI for all eight (if they sell at the price I want, of course this may not happen).  This way I can make a quick profit ROI as well as still mine the coins and see what happens with price and difficulty.  

I would not do a "pre-sale" on amazon or ebay.  12 years of experience as an ebay seller just tells me this is a great way to get a lot of negative feedback.   What happens when you try and sell your X11 miner on ebay, then bitmain sends you some DOA bullshit? Wait until the machine is in your possession to sell it, is my advice.

I bought a few of D3s from the first batch.  With so much FUD about profitability, what do you think about selling it for $6k or so for instant 100% gain?

You might make more money by running it in the long run, but there will be lot of uncertainties such as difficulty increase and price change of X11 coins, mainly DASH.  It might make sense to just flip it for quick profit for almost no work rather than trying to hodl and mine with it.

edit:  I also have some L3+ that is coming in late August.  Same question:  flip it or mine with it?

We do.

Depends on how soon you can get either one. L3+ has already sold several batches, and D3 only a few. If you can get a D3 ordered in the next batch then it would be better than getting an L3+ in the next batch.

around 28-30 mh/s on ethereum. most likely to be a clone of the 1080. not the ti.

1080ti = 36mh/s
vega = 28-30mh/s

1080ti > vega

I ordered an L3+ have been using it for a month. The difficulty is going up like crazy. By the time September batch starts shipping the machines wont be generating much. Besides that I have noticed this with Bitmain products for years now. And FYI Batch 1 of this miner was sold out in minutes. Another batch will be coming up soon. It says that one machine makes over $200 per day but by the time we get it it would make less than half of that.