I'm not running a huge farm, so I'm more than likely going to cut my losses prior to the Havlening. Won't sell off my miners until a few weeks after the Halving, just to see how much more difficult things get.
I have a feeling in last few weeks pevious gen will take a decent jump down. Current gen... not sure on it unless something else better comes out.
I would not wait till last minute. I sold mine a bit back on last gen, and invested in coins. So far I did much better then I would have mining older gear (I have normal not cheap electricity)
I think the current 14 or 16 nm miners are already out. They are being "tested" by the manufacturers to mine a lot of coins.
Most are not public on it though. Only one I think you can buy right now is B11 and it is not the final perfected stats, it was pretty far off on what they made and what they showed on site.
All the other new ones still internal. And we still don't know much about them.