You also have to ascribe an accurate decisional weight to the warranty from Bitmain. It's pretty much understood that they'll do as much as they can to deny all warranty claims, and if you read the not-so-fine print basically any feasible issue is not covered under the warranty. I would not consider a Bitmain warranty as a factor in any risk assessment. The few problems they will actually work with you on, once you factor in hassle, arguments, shipping to China and the associated revenue loss of extended downtime, it'd be cheaper to solve the problem with parts off eBay or something. If you happen to have a hashboard that fails without burning something (and therefore voiding warranty) might be a bit tricky, but what are the odds of that?
I noticed that each miner seems to have its own personality (frequency) that it runs most efficiently. You just have to find it and run it. The warranty is an issue that you are going to have to decide.
